Building Healthy Soils in Vegetable Gardens: Cover Crops Have Got It Covered Part II: Types of Cover Crops – Non-legumes, Legumes, and Mixtures

Megan M. Gregory, Blog Contributor, Cover Crop Nerd, and Graduate Research Assistant, Cornell University

This article is part of a four-part series about cover cropping in vegetable gardens.  Stay tuned for Part III next week. 

Vegetable gardeners are turning to cover crops to improve soil quality, add nitrogen (N) to the soil through legume N fixation, suppress weeds, and attract beneficial insects in their gardens.  In this article I’ll introduce several groups of cover crops.  Cover crop species can be broadly grouped into non-legumes (those that do not fix N, but take up and recycle nutrients left in the soil) and legumes (which fix N).   Mixtures of non-legumes and legumes may offer the benefits of both types of cover crops.

Non-legume cover crops

Non-legume cover crops include species in several plant families:

Fig. 1.  Examples of non-legume cover crops used in vegetable gardens (Photo credits: M. Gregory)
 pic 5  pic 6  pic 7
Fig. 1a.  Oats (Avena sativa) is a winter-kill cover crop in USDA Zones 7 and cooler.  It is usually planted in late August, and dies with the first hard frosts.
Fig. 1b.  Winter rye (Secale cereale) is a hardy over-wintering cover crop.  It can be planted in September or October, and produces large amounts of biomass by May.
Fig. 1 c.  Buckwheat (Fagopyrun esculentum) is a fast-growing summer cover crop, suitable for planting between spring and fall vegetable crops.

Benefits of non-legumes: 1, 2

  • Prevent erosion – Non-legumes establish and grow quickly, provide rapid soil cover, and have dense, fibrous root systems that hold soil in place.
  • Build soil organic matter – Non-legumes produce large amounts of biomass, which contributes to soil organic matter.3
  • Retain and recycle nutrients – Non-legumes take up nutrients left in the soil after vegetable harvest, which prevents them from being leached out of the garden during heavy spring rains.
  • Suppress weeds – With their vigorous growth and high biomass, non-legumes can successfully compete with weeds, even in fertile soils. Some non-legumes (winter rye, sorghum-sudangrass, and Brassicas) also release chemicals that inhibit weed germination and growth.  Residues of grass cover crops also provide a weed-suppressive mulch that lasts much of the growing season.
  • Disease management — Some Brassicaceae cover crops also release chemical compounds that may help control soil-borne pathogens and parasites(e.g., fungi, nematodes) upon incorporation. Winter rapeseed (Brassica napus) greatly reduced Rhizoctonia damage and Verticillium wilt in potato crops.1, 2

Drawbacks and constraints of non-legumes:

  • Slow nutrient supply and/or N immobilization — Non-legumes have lots of carbon (C) relative to N during growth, which causes them to decompose slowly after mowing or incorporation. As a result, nutrients in non-legume residues may not be available to vegetable crops quickly. If non-legume residues are incorporated into the soil, they may actually immobilize (“tie up”) N for a few weeks as decomposer microbes take up soil N to balance the large amount of C in the plant residues they’re breaking down.1  For this reason, it’s best to wait several weeks after incorporating a non-legume before planting vegetable crops.

Legume cover crops

Legume cover crops include field peas (Fig. 2a) crimson clover (Fig. 2b), hairy vetch (Fig. 2c), and cowpeas.  They provide many of the same benefits of non-legumes, with the additional benefits of nitrogen fixation and feeding pollinators.

Fig. 2.  Examples of legume cover crops used in vegetable gardens  (Photo credits: M. Gregory)
 pic 8  pic 9  pic 10
Fig. 2a.  Field peas (Pisum sativum) can be planted as a winter-kill or early spring cover crop.  It should only be planted in full sun, as this legume performs poorly in shaded areas.4 Fig. 2b.Crimson clover (Trifolium incarnatum) over-winters in Zones 7 and up, and can be used as a summer or winter-kill cover crop in cooler zones.  Crimson clover is a high biomass producer and is quite shade-tolerant.4 Fig. 2c.  Hairy vetch (Vicia villosa) is the hardiest legume, and will over-winter in even the northernmost parts of the US.  It is an excellent legume for adding fixed N to the soil.4


Additional Benefits of legumes:

pic 11
Figure 3. A bumblebee visits a crimson clover flower in a community garden. Photo credit: M. Gregory.
  • Nitrogen fixation – Legume cover crops add ‘new’ nitrogen (N) to the soil through N fixation, which occurs when N-fixing bacteria in legume roots take N from the air and convert it to a form the plant can use. When legume residues break down, this N is added to the soil for food crops.5
  • Build soil organic matter and soil quality – While legumes don’t usually produce as much biomass as non-legumes, they also help build soil organic matter.6, 7 Legumes are also excellent soil conditioners, because legume roots ooze sugars that stick soil particles together in larger crumbs, or aggregates.8, 9  This helps the particles fit together loosely, making for a soft, porous soil.
  • Attract beneficial insects – Many legume species provide resources for beneficial insects. Crimson clover provides pollen and nectar for native pollinator bees (Fig. 3), and both crimson clover and hairy vetch host predators such as lady beetles, which eat many pest insects.1


Drawbacks and constraints of legumes: 1, 3

  • Slow growth, lower biomass — Legumes establish and grow more slowly than non-legumes, and usually produce lower biomass.
  • Less weed suppression — Legumes may not suppress weeds as effectively as non-legumes, particularly in soils with high N fertility. In Brooklyn gardens, legumes suppressed weeds in soils with low to moderate N fertility, but not in soils with high N fertility.4  Legume residues break down quickly, so weed control by legume mulch may be short-lived.
  • Seed cost — Legume seeds are more costly than non-legumes.


Cover crop mixtures

Mixtures of non-legumes and legumes often combine the benefits of both types of cover crops.

Benefits of nonlegume/legume mixtures:

  • Produce large biomass and suppress weeds effectively — In many cases, cover crop mixtures provide more complete soil cover, greater biomass production, and more effective weed suppression than plantings of just one species.1, 3  This is because mixtures of grasses and legumes use water, nutrients and sunlight very efficiently due to complementary root systems and growth habits.  Grasses (like rye) also provide support for viny legumes (like hairy vetch), which allows the legume to access more light.
  • Increase N fixation — Planting legumes with grasses may enhance N fixation. Grasses out-compete legumes for soil N, forcing the legume to rely on N fixation.  As long as the grass doesn’t suppress legume biomass (see below), this can increase the total amount of N fixed.  Promising grass/legume mixtures for N fixation include rye/vetch and Japanese millet/cowpea.10
  • Optimize nutrient cycling and nutrient supply to crops — Mixtures provide the benefits of N ‘scavenging’ by non-legumes and N additions by legumes.1 At maturity, grass-legume mixtures often have an ideal C:N ratio of 25:1 – 30:1, which promotes a steady release of N for vegetable crop use as the cover crop plants decompose.  N-rich legume residues prevent N tie-up that can occur when incorporating pure grass residues, while C-rich grass residues slow the breakdown of legume residues such that N is released at a rate that vegetable crops can use through the growing season.2, 11
Fig. 4.  Examples of grass/legume mixtures used in vegetable gardens  (Photo credits: M. Gregory)
 pic 12  pic 13
 Fig. 4a.  Oats/ Field peas is a common winter-kill or early spring mixture.  It should only be planted in full sun.  Since oats may suppress field pea biomass and total N fixed,4 try seeding the field peas at a higher rate. Fig. 4b.  Rye/ hairy vetch is an excellent over-wintering mixture.  The hairy vetch ‘climbs’ the rye, which allows the legume to access more light.  In Brooklyn gardens, rye/vetch mixtures produced the highest biomass of any cover crop combination.4

Drawbacks and constraints of nonlegume/legume mixtures:

  • Reduced N fixation if nonlegume out-competes the legume – Mixing a non-legume with a legume may decrease the total amount of N fixed if the non-legume suppresses legume growth and biomass. This occurs in mixtures of: oats/field peas,4, 12 rye/crimson clover,4 and sorghum-sudangrass/cowpea.10  Seeding the legume at a higher rate may result in a more even distribution of nonlegume and legume biomass – gardeners can experiment to find the relative seeding rate that works best in your soil.


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Understanding the benefits and limitations of non-legumes, legumes, and mixtures is a great starting point for selecting cover crops to plant in your garden.  For guidance on choosing specific cover crops based on your vegetable crop rotation, management goals, and soil and light conditions, see Part III: Selecting Cover Crops for Vegetable Gardens.



(1) Clark, A.  2007.  Managing cover crops profitably, 3rd ed. Sustainable Agriculture Network, Beltsville, MD.  Accessed online at:, 7 December 2014.

(2) Treadwell, D., N. Creamer, and K. Baldwin.  2010.  An introduction to cover crop species in organic farming systems.  Accessed online at:, 7 December 2014.

(3) Snapp, S. S., S. M. Swinton, R. Labarta, D. Mutch, J. R. Black, R. Leep, J. Nyiraneza, and K. O’Neil.  2005.  Evaluating cover crops for benefits, costs and performance within cropping system niches.  Agronomy Journal 97(1):322-332.

(4) Gregory, M. M., L. E. Drinkwater.  In preparation.  Developing cover cropping practices to improve soil quality, nutrient cycling, and weed suppression in urban community gardens.

(5) Drinkwater, L. E.  2011.  It’s elemental: How legumes bridge the nitrogen gap.  The Natural Farmer, Summer 2011, pp. B-1 – B-6.  Northeast Organic Farming Association, Barre, MA: Accessed online at:, 6 December 2014.

(6) Sainju, U. M., B. P. Singh, and W. F. Whitehead.  2002.  Long-term effects of tillage, cover crops, and nitrogen fertilization on organic carbon and nitrogen concentrations in sandy loam soils in Georgia, USA.  Soil & Tillage Research 63(3-4):167-179.

(7) Kong, A. Y. Y., J. Six, D. C. Bryant, R. F. Denison, and C. van Kessel.  2005.  The relationship between carbon input, aggregation, and soil organic carbon stabilization in sustainable cropping systems.  Soil Science Society of America Journal 69(4):1078-1085.

(8) Puget, P., L. E. Drinkwater.  2001.  Short-term dynamics of root- and shoot-derived carbon from a leguminous green manure.  Soil Science Society of America Journal 65(3):771-779.

(9) Haynes, R. J., M. H. Beare.  1997.  Influence of six crop species on aggregate stability and some labile organic matter fractions.  Soil Biology & Biochemistry 29(11-12):1647-1653.

(10) Drinkwater, L. E.  2011.  A holistic view: Leguminous cover crop management in organic farming systems.  The Natural Farmer, Summer 2011, pp. B-20 – B-24.  Northeast Organic Farming Association: Barre, MA. Accessed online at:, 6 December 2014.

(11) Teasdale, J. R., A. A. Abdul-Baki.  1998.  Comparison of mixtures vs. monocultures of cover crops for fresh-market tomato production with and without herbicide.  HortScience 33(7):1163-1166.

(12) Schipanski, M. E., L. E. Drinkwater.  2012.  Nitrogen fixation in annual and perennial legume-grass mixtures across a fertility gradient.  Plant Soil 357(1-2):147-159.


Garden Site Selection

Shawn Banks: Extension Blog Contributor
Johnston County Extension Agent/Educator
North Carolina State University

As an extension agent one question I often get asked by new gardeners is, “Where do I put a vegetable garden in my yard?” That leads to a lot more questions, but let’s answer the where question first. There are four basic considerations when selecting a garden site.

narrow strip of garden vegetables in a backyard area

The first thing to consider is the need for direct or full sunlight. Most vegetables need a minimum of six to eight hours in order to produce a crop. However, the more sunlight they get the more bounteous the harvest will be. If there isn’t a spot in the yard that receives full sun all day, then the question becomes, is it better to have shade in the morning or in the evening? Morning sun will dry the dew from the leaves, reducing the chance of fungal diseases infecting the leaves.

person watering vegetable garden with a hoseSpeaking of dew, the next consideration is water. How close is the water source to the vegetable garden. Many vegetables need to have consistent moisture. That means a water source should be easy to access to keep the soil moist throughout the growing season. The further the water is from the garden, the less likely it is that the garden will get watered on a regular basis. Have you ever wondered why the tomatoes crack, or the radishes split? One of the most common reasons is that the soil was very dry and then it rained a lot and the plant was trying to store as much water as possible, causing the cracks and splits

Raised beds with vegetables growing in themAnother consideration is airflow. Many foliar diseases are caused by fungal pathogens. Most fungi need water standing on the leaf for eight or more hours before they can infect the leaf. Good airflow will dry the leaves out before the fungi can infect the plant. A hedge, a solid fence, or even a house may obstruct airflow. Another way to obstruct airflow is to plant too close together, but that is a discussion for another time.

A trellis in the back of a raised bed supports peasLastly comes the phrase “out of sight, out of mind”. This is very true for a vegetable garden. When selecting where to place the garden, consider ease of access. Many people find that when the garden is way in the backyard, they don’t tend it often enough. The soil dries out. The weeds take over. The crops don’t get harvested in a timely manner. In short, the garden doesn’t succeed. Select a garden site that is close enough that you will see it and want to tend to it.

These four site characteristics are the most important when selecting the location for a vegetable garden. Remember, a vegetable garden site needs a minimum of eight hours of direct sunlight, consistent moisture, good airflow, and easy access. A site with all four of these characteristics will ultimately produce more, have fewer problems with fungal diseases, and be better taken care of because it is visited more frequently and loved.

Keep in mind that if you don’t have anywhere in your yard that works, many options, such as container gardens, can help you have a productive garden anywhere.

Garden Site Selection pdf

Building Healthy Soils in Vegetable Gardens: Cover Crops Have Got It Covered Part I: Introduction to Cover Cropping

Megan M. Gregory, Blog Contributor, Cover Crop Nerd, and Graduate Research Assistant, Cornell University

This article is part of a four-part series about cover cropping in vegetable gardens. Stay tuned next week for Part II

What are cover crops, anyway?

cover crop
Figure 1. Rye and vetch cover crop in a community garden plot in May, just before it was cut down and mulched in preparation for planting vegetables. Photo credit: M. Gregory. 

Cover crops are close-growing plants sown in rotation with food crops, or inter-seeded between food crops to cover bare ground.  They are not harvested, but rather are planted to improve soil quality and provide other benefits for crop production and the environment.  Before planting the next vegetable crop, most cover crops need to be cut down.  The shoots can be chopped (or mowed) and left as mulch on the soil surface, or incorporated into the soil.

There is a large body of research supporting the use of cover crops on organic and sustainable farms.1  However, vegetable gardeners can successfully plant and manage cover crops with hand tools, and reap the benefits of this practice for their soil and crops.2

Why should I plant a crop that I’m not going to harvest?

Cover crops provide many benefits for future vegetable crop production, and for the garden agro-ecosystem as a whole.  Incorporating cover crops in vegetable rotations may:

  • Increase soil organic matter levels, and therefore improve soil quality. As cover crop roots and shoots decompose, they build soil organic matter.  This improves soil structure and water-holding capacity (Fig. 2), and increases slow-release nutrient reserves.3  Fresh cover crop residues also nourish beneficial soil fauna (bacteria, fungi, worms, etc.) that improve soil tilth and aeration, recycle plant and animal wastes, and release nutrients for crops to use.
  • Provide nitrogen for future food crops through legume nitrogen fixation. Cover crops in the legume family (e.g., beans, peas, clovers, and vetches) add “new” nitrogen (N) to the soil.  Legumes host N-fixing bacteria in bumps on their roots, also called nodules (Fig. 3).  These bacteria take N from the air and convert it to a form the legume can use .  When the plant decomposes, the fixed N also becomes part of the soil organic matter.  Eventually, this N is released by microbes for crop uptake.4
  • Improve nutrient retention and recycling. Over-wintering cover crops take up extra nutrients at the end of the growing season, which would otherwise be lost to leaching (when nutrients dissolve in rainwater and drain below the root zone, making the nutrients unavailable for plants).  Over-wintering grasses like rye reduce N leaching by about 70% compared to bare soil.5
  • Suppress weeds. Growing cover crops reduce weed growth through competition (e.g., for space, light, moisture, and nutrients) and allelopathy (releasing chemicals that inhibit other plants).  After , the cover crop mulch can prevent weed seedling emergence through the growing season.6
  • Attract beneficial insects. Cover crops often provide important resources (such as nectar and pollen and over-wintering habitat) for beneficial insects, including pollinator bees and natural enemies of insect pests like ladybugs and lacewing.1
  • Increase or maintain crop yields with less inputs. Well-managed cover crops can improve vegetable crop yields, or reduce the amount of fertilizer needed to obtain good yields.7-10


pic 2
Figure 2. Demonstration illustrating the effect of soil organic matter (SOM) on water-holding capacity. Photo credit: Megan Gregory
  • On the left is soil from an urban garden that received a rye/vetch cover crop for more than five years, and therefore has high SOM.
  • On the right is soil from a garden that never received cover crops, and has lower SOM.
  • This photo was taken 30 minutes after pouring equal amounts of water through the soils. The high-OM soil held most of the water, while much water drained through the low-OM soil. Since both soils were of similar texture, the difference in water-holding capacity can be attributed to the SOM.




nodules on roots of cover crops
Figure 3. Nodules on the roots of legume cover crops: crimson clover (left) and hairy vetch (right). The nodules host nitrogen-fixing bacteria in the genus Rhizobia, which convert atmospheric nitrogen into plant-available forms. Photo credits: M. Gregory.

pic 3




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Vegetable gardeners have a number of cover crop options suited to different seasonal niches, management goals, and environmental conditions.  To learn about the main groups of cover crops and how to select cover crops for your garden, see Part II (Types of Cover Crops) and Part III (Selecting Cover Crops).


(1) Clark, A.  2007.  Managing cover crops profitably, 3rd ed. Sustainable Agriculture Network, Beltsville, MD.  Accessed online at:, 7 December 2014.

(2) Gregory, M. M. and L. E. Drinkwater.  In preparation.  Developing cover cropping practices to improve soil quality, nutrient cycling, and weed suppression in urban community gardens.

(3) Snapp, S. S., S. M. Swinton, R. Labarta, D. Mutch, J. R. Black, R. Leep, J. Nyiraneza, and K. O’Neil.  2005.  Evaluating cover crops for benefits, costs and performance within cropping system niches.  Agronomy Journal 97(1):322-332.

(4) Drinkwater, L. E.  2011.  It’s elemental: How legumes bridge the nitrogen gap.  The Natural Farmer, Summer 2011, pp. B-1 – B-6.  Northeast Organic Farming Association, Barre, MA.  Accessed online at:, 6 December 2014.

(5) Tonitto, C., M. B. David, and L. E. Drinkwater.  2006.  Replacing bare fallows with cover crops in fertilizer-intensive cropping systems: A meta-analysis of crop yield and N dynamics.  Agriculture Ecosystems & Environment 112(1):58-72.

(6) Schonbeck, M.  2011.  How cover crops suppress weeds.  Accessed online at:, 6 December 2014.

(7) Abdul-Baki, A. A., J. R. Teasdale, R. Korcak, D. J. Chitwood, and R. N. Huettel.  1996.  Fresh-market tomato production in a low-input alternative system using cover-crop mulch.  HortScience 31(1):65-69.

(8) Abdul-Baki, A. A., J. R. Stommel, A. E. Watada, J. R. Teasdale, and R. D. Morse.  1996.  Hairy vetch mulch favorably impacts yield of processing tomatoes.  HortScience 31(3):338-340.

(9) Abdul-Baki, A. A., J. R. Teasdale, R. W. Goth, and K. G. Haynes.  2002.  Marketable yields of fresh-market tomatoes grown in plastic and hairy vetch mulches.  HortScience 37(6):878-881.

(10) Abdul-Baki, A. A., J. R. Teasdale.  1997.  Snap bean production in conventional tillage and in no-till hairy vetch mulch.  HortScience 32(7):1191-1193.

Pruning Overgrown Apple Trees

Ward Upham: Extension Blog Contributor
Extension Associate – Home Horticulture Rapid Response Coordinator
& Extension Master Gardener Coordinator
Kansas State University Extension


Apple trees that are not pruned for several years will often produce so many branches that very little energy is left for fruit production. Overgrown apple trees are also difficult to harvest and spray. Gardeners who have such a tree are often at a loss as to how to get it back in shape.

Often the best (tongue-in-cheek) recommendation s for such a tree is to make one pruning cut at ground level and start over with a new tree. However, trees may have sentimental value that will make revitalization worth the time and effort. Realize that this will be a multi-year process because no more than 30 percent of the tree should be removed in one year. Here are some steps to follow:

  1. Remove all dead wood. This does not count toward the 30 percent.
  2. Remove suckers from the base of the tree.
  3. Choose approximately six of the best branches to keep as scaffold branches. Remove all others. Branches should be cut flush to the branch collar. The collar is that natural swelling that occurs where a branch connects to the trunk or to a larger branch. Removing the collar would leave a larger wound that would take additional time to heal. Do not paint wounds. Research has shown that wounds heal more quickly if left open. Candidates for removal include branches with narrow crotch angles, which are more likely to break in wind and ice storms, and those that cross branches you will save. This may be all that is possible the first year if the 30 percent threshold has been reached.
  4. Thin the branches on each scaffold branch. Remove crowded branches to open up the tree to light and allow humidity to escape. Shorten each scaffold branch by cutting back to a side branch. When you are through, the tree should have enough wood removed so that a softball can be thrown through the tree.

Severe pruning often will cause an apple to tree to produce vigorous side shoots from the trunk, called water sprouts. Main branches will also produce suckers that grow straight up. The suckers and water sprouts should be removed throughout the growing season so the center of the tree stays open.

In the case where a tree cannot be saved but you would like to preserve the apple tree variety, consider grafting. Scions taken from the old tree can be grafted onto a new rootstock to form a new tree. If you are not able to do so yourself, contact a local fruit tree nursery to find someone who may be able to help.

Pruning Overgrown Apple Trees pdf

A 19th Century Garden Hero: Hero or villain today?

John Porter: Extension Blog Contributer
Extension Agent, Ag and Natural Resources
West Virginia University

There’s been much ado in the press and on social media about the use of Genetically Modified Organisms (GMOs) in the food system.  While there is a scientific consensus on their safety, many still reject their use. While the controversy rages on, an innocent bystander has taken fire, mainly from the spread of misinformation on social media.  It seems that simple hybrids, produced through a selective, yet natural, breeding process have been mislabeled as genetically modified.  These misinformation sources point to heirlooms as the only non-modified (and thus safe) source of food.  The thought is that since the development of a hybrid is directed by humans, they are genetically modified.  This simply isn’t the case.

The truth of the matter is that all of the food crops that we plant have been modified at some point in history through human intervention, whether purposeful or not.  The simple act of seed saving is a selective breeding process selecting for the best and the tastiest. So even heirlooms are modified through human interaction.  The comparison of a hybrid to a GMO is starkly false.  I once saw someone explain it this way:  breeding a hybrid is like crossing a beagle and pug, making a GM crop is like crossing a potato and a fish.  While it is a simplistic comparison, it does make it a little easier to understand.

Many of the heirlooms we now have today were developed by breeders over the last century or so.  No one man had such an impact on agriculture as Luther Burbank, who was a prolific plant breeder and a well-known national hero.  However, in today’s anti-science fervor, would he be considered more of a villain than a hero?  That was the topic of one of my recent newspapers articles. Read more about Luther Burbank, 19th century garden hero.


Managing Diseases without Fungicides: A Focus on Sanitation (A Visiting Professor feature)

Submitted by:
Nicole Ward Gauthier,
University of Kentucky Extension Plant Pathologist
PEOPLE: University of Kentucky Department of Plant Pathology Website
Kentucky Diseases of Fruit Crops, Ornamentals, & Forest Trees on Facebook
Amanda Sears, Kentucky Extension Horticulture Agent
Madison County Cooperative Extension Website

Alternatives to Fungicides

When diseases occur in urban landscapes, it is often presumed that fungicides are the most important and effective disease management tools available. However, a good sanitation program can help reduce the need for chemical controls and can improve the effectiveness of other practices for managing disease. This often-overlooked disease management tool reduces pathogen numbers and eliminates infective propagules (inoculum such as fungal spores (figure 1c) , bacterial cells; virus particles; and nematode eggs) that cause disease.

fig 1b marigold botrytis 1525420 (MC Shurtleff, UIll bugwd) (640x412)
Figure 1a. Marigold blossom infected with Botrytis
  Figure 1b. Pathogen levels can build up on marigold flowers if diseased tissue is left in the landscape

Figure 1b. Pathogen levels can build up on marigold flowers if diseased tissue is left in the landscape
close up of infecting spores
Figure 1c. Infecting spores on plant surface

Certain foliar fungal and bacterial leaf spots can become prevalent during rainy or humid growing seasons. When disease management is neglected, pathogen populations build-up and continue to increase as long as there is susceptible plant tissue available for infection and disease development (Figures 1a-c). Infected plant tissue infested soil and pathogen inoculum all serve as sources of pathogens that can later infect healthy plants.

Figure 2. Fallen leaves can serve as a source of inoculum (fungal spores) for additional infections. Many pathogens overwinter in fallen debris and then produce infective spores the following spring.

Reduction of pathogens by various sanitation practices can reduce both active and dormant pathogens. While actively growing plants can provide host tissue for pathogen multiplication, dead plant material (foliage, stems, roots) can harbor overwintering propagules for months or years (Figure 2).

These propagules can travel via air/wind currents, stick to shoes or tools, or move with contaminated soil or water droplets. Thus, prevention of spread of pathogens to healthy plants and the elimination of any disease-causing organisms from one season to another are the foundations for a disease management program using sanitation practices.

Sanitation Practices

Elimination and/or reduction of pathogens from the landscape results in fewer pathogen propagules. The following sanitary practices can reduce amounts of infectious pathogens:

Figure 3a. Cankers are common overwintering sites for disease-causing pathogens
  • Remove diseased plant tissues from infected plants. Prune branches with cankers (Figure 3a) well below the point of infection (Figure 3b). Cuts should be made at an intersecting branch. Rake and remove fallen buds, flowers, twigs, leaves, and needles.
Figure 3b. Remove infected branches, making cuts well below points of infection
  • Disinfest tools used to prune galls and cankers.  Cutting blades should be dipped into a commercial sanitizer, 10% Lysol disinfectant, 10% bleach, or rubbing alcohol between each cut.
  • If using bleach, rinse and oil tools after completing work, to prevent corrosion.
  • Discard perennial and annual plants that are heavily infected and those with untreatable diseases (e.g. root rots, Figure 4; and vascular wilts).  Dig up infected plants to include as much of the root system as possible, along with infested soil.

infected plant                           imag

Figure 4. Heavily infected plants or those with untreatable diseases, such as black root rot (images left and right), should be removed from the landscape.   

  • Trees and shrubs infected with systemic diseases (e.g. Dutch elm disease, Verticillium wilt, bacterial leaf scorch) that show considerable dieback should be cut and the stump removed or destroyed (e.g. by grinding).
  • If infected plants are to be treated with fungicides, prune or remove infected tissue (flowers, leaves) and debris to eliminate sources for spore production or propagule multiplication.  This should be done before fungicide application. Fungicide effectiveness may be reduced when disease pressure is heavy, which can result when pathogen levels cannot be reduced sufficiently by chemical means (fungicides).
  • Discard fallen leaves, needles (Figure 5), prunings, and culled plants. Never leave diseased plant material in the landscape, as pathogens may continue to multiply by producing spores or other propagules.  Infected plant material should be buried, burned, or removed with other yard waste.

pathogen 1       pathogen 2

Figure 5.  Black fruiting structures of the pine needlecast pathogen contain spores (images left and right). Removal of infected plant tissue helps reduce amounts of inoculum in the landscape.

  • Do not compost diseased plant material or infested soil because incomplete composting (temperatures below 160˚ F) may result in survival of propagules.
  • Homeowners should be cautious about storing diseased limbs and trunks as firewood or using the woodchips as mulch.  For example, wood from trees infected with Dutch elm disease should be debarked before placing in a firewood pile.
  • Remove weeds and volunteer plants to prevent establishment of a “green bridge” between plants.  A green bridge allows pathogens to infect alternate hosts until a more suitable one becomes available.  Be sure to remove aboveground parts AND roots.
  • Soil from container-grown plants should not be reused from one season to the next because pathogens can survive in soil.

Additional Resources:

University of Kentucky Extension Plant Pathology Publications

Photo credits:

R.K. Jones, North Carolina State University (Fig. 1A), courtesy
M.C. Shurtleff, University of Illinois (Fig. 1B), courtesy
David Cappaert, Michigan State University (Fig. 1C), courtesy
Theodor D. Leininger, USDA Forest Service (Fig. 2), courtesy
Joseph O’Brien, USDA Forest Service (Fig. 3, right), courtesy
Elizabeth Bush, Virginia Tech (Fig. 4, left), courtesy
Bruce Watt, University of Maine (Fig. 4, right), courtesy
Andrej Kunca, National Forest Centre, Slovakia (Fig. 5, left), courtesy
Robert L. Anderson, USDA Forest Service (Fig. 5, right), courtesy
John R. Hartman, University of Kentucky (Fig. 3, left)

 pdf  Managing Diseases Without Fungicides

A tale of two winters

I’m not sure we’ve ever been quite so ready for the calendar to turn to March. That’s assuming, of course, you live somewhere east of the Rockies. For people on the west coast, the sentiment is probably, “When are those people back East ever going to quit b-tching about their weather…” While I was dealing with 10” of snow and 25 mph winds whipping up 3’ deep drifts on Super Bowl Sunday, my friends back home in Washington state were mowing their grass. At this point I don’t even remember what my lawn looks like.

I have to confess that I thought winter 2014 was an anomaly and that we wouldn’t see weather that cold again any time soon, if ever. Boy, did I get wrong number. While winter 2015 is not exactly a carbon copy of 2014, I’m not sure most of us can tell the difference. In case dealing with sub-zero wind-chills for weeks on end wasn’t torture enough, I dug into the weather records from our automated Michigan EnviroWeather network to see how the past couple of months stacked up. To keep things simple I queried the records for the past twenty Januaries and Februaries. I just include those months since we don’t have any data for this March yet and those are the months we typically get our coldest weather, though we occasionally also get sub-zero in late December.

Over the last 20 years the past two winters have been by far the coldest, and it’s not even close. Over the previous 18 years the average daily low temperature for January and February was 17.0 deg. F. In 2014 the average low was 5.9 deg. F; this year it was 5.8 deg. F.

Daily low temperatures in Jan. and Feb. of 2014 and 2015 were more than 11 degrees below the average of the previous 18 years.
Daily low temperatures in Jan. and Feb. of 2014 and 2015 were more than 11 degrees below the average of the previous 18 years.

Not only was it colder on average but we’ve had more extreme cold events in the past two years as well. Between 1996 and 2013 we averaged less than one day per year with low temperatures below -10 deg. We were below -10 deg. F on eight days this winter and nine days last winter. The bottom end of our USDA Hardiness Zone 5 is -15 deg. F. We have been below that mark five times this winter, compared to twice last year and zero times in the previous 18 years.

Over the past 20 years we rarely dipped below -10 F. We've been colder than -10 seventeen times in the past two winters.
Over the past 20 years we rarely dipped below -10 F. We’ve been colder than -10 seventeen times in the past two winters.

Obviously this data is specific to mid-Michigan, but I suspect most locations in the Midwest and Northeast will have similar stories to tell. So what does all this mean? For one, our hardiness zones are what they are for a reason. Folks that like to ‘push their zones’ (you know who you are), have gotten away with it with impunity for nearly 20 years. This winter and last were time to pay the piper.

The owner of this Cedrus deodora 'Polar winter' (zone 6) had gotten away with pushing their zone for 10 years before things came to grinding halt in 2014.
The owner of this Cedrus deodora ‘Polar winter’ (zone 6) had gotten away with pushing their zone for 10 years before things came to grinding halt in 2014.

The other take home lesson is that climate doesn’t consistently move in one direction. Even if we’re in a period of general warming, extreme events will still occur. This is important to remember as we think about planning for projected future climates. We have seen the appearance of several climate-change friendly plants lists. In some cases the authors have simply looked at projected climate zones and moved plant selections northward. The problem with this approach is tree survival is based on extremes, not on averages.