After writing about the unusually bad scourge of Japanese Beetles earlier in the month, I thought I’d continue on down the “garden bugs” path. The Japanese Beetles have died down, but now we have oodles of these pretty black and yellow-spotted waspy things around. They’re everywhere, and in large numbers. I planted some buckwheat over our potato garden bed, and it is covered up with them. The point of the buckwheat was as a primo late-season nectar source for our honeybee hives as they prepare for winter. Blooming for the last week or two, I kept checking it expecting to see happy bees, feasting away. Nada. Just the wasps.
Intriguing. A brief googling revealed the wasp to be Scolia dubia, one of the “digger wasps.” They rarely sting, and better yet -their larvae are parasites of Japanese Beetles! All that swooping around over our so-called lawn is apparently the mating dance, then the female digs into the soil to find the grubs. After stinging the grub, she lays an egg…and you see where this is going. Cozy winter grub cocoon for the pupating larvae!
Back to the bed of gourmet buckwheat. I’m thrilled to see all those wasps feeding on the nectar. Eat, dig, and be merry, ladies! But what about the honeybees – seemingly ignoring this glorious patch of buckwheat planted just for them? I don’t need any more picky eaters…aren’t our two dinner-snubbing dogs enough? So I asked Dr. Richard Fell, legendary Apiculture faculty here at Virginia Tech, about this mystery. “Honeybees only work buckwheat in the morning” sayeth Rick. Went out this morning and observed that buckwheat is indeed the breakfast of champions. The entire patch was literally humming with multiple species, including loads of honeybees. I’d only been checking in the evening.
So my post apparently isn’t breaking news. Just came across this as I checked my Scolia spelling. Sounds like they had beetles galore in Maryland as well this summer.
If you’re not familiar with Dr. Michael Raupp, Entomologist and Extension Specialist at University of Maryland, he’s awesome, and his “Bug of the Week” blog is a must. His September 1 post reviews the digger wasp/japanese beetle relationship as well, with more factoids and a lovely video featuring writhing grubs. http://bugoftheweek.com/blog/2014/9/1/white-grubs-beware-the-blue-winged-digger-wasp-iscolia-dubiai-has-arrived
Soil solarization is regarded as an environmentally friendly alternative to pesticides for controlling nematodes, weeds and disease. Sheets of plastic (generally clear) are spread over the ground and solar energy heats the soil underneath to temperatures as high as 55C (or 131F). Since the soil environment is usually insulated from temperature extremes, the organisms that live there are unlikely to be resistant to heat stress.
This is a practice best suited to agricultural production, where monocultures of plants have attracted their specific diseases and pests. Decades of research have shown success in controlling pests in greenhouses, nurseries, and fields. But there’s a down side to this chemical-free means of pest control.
It shouldn’t be surprising that beneficial soil organisms, in addition to pests and pathogens, are killed by solarization. Studies have found that soil solarization wipes out native mycorrhizal fungi and nitrogen-fixing bacteria. One expects that other beneficial microbes, predacious insects, and parasitoids living in the soil (but so far unstudied) would be eliminated as well.
This may be an acceptable loss to those who are producing crops; soil can be reinoculated with mycorrhizal fungi, for example. But for those of us caring for our own gardens and landscapes, this is literally overkill. (And consider that most of us probably have trees and shrubs whose fine roots extend over our entire property.)
So this spring, instead of solarizing your soil, consider some less drastic measures of pest and disease control. Minimize soil disruption to preserve populations of desirable microbes. Plant polycultures (more than one species) in your vegetable garden, or at least practice crop rotation. Protect and nourish vegetable gardens with compost. Use coarse organic mulches, which provide habitat for beneficial insects and spiders, in landscaped areas. Above all, try to treat your soil as the living ecosystem it is, rather than a war zone.
One of the products that I often hear gardeners raving about are their fertilizer / pesticide combination spikes which are supposed to not only feed your plants, but also kill all of the insects which attack them. I, personally, have not used these products, but I’m generally the kind of person who says “If it works for you then keep using it”. Still, these spikes bug me a little. Here’s why.
First of all I should point out that I’m not opposed to fertilizer spikes by themselves. I’m a little concerned that fertilizer should be spread out instead of concentrated in one place, but still, I don’t consider them that bad. The insecticides used for these spikes is where I have the problem. Once upon a time these spikes were made with a chemical called disulfoton (aka disyston) which is bad news. It’s a water soluble chemical which is highly toxic to people. If you have an old package of fertilizer / insecticide spikes around there’s a good chance they were made with this chemical. Do yourself a favor and get rid of them. This stuff is really toxic and not to be messed with. On the other hand, if you’ve purchased fertilizer / insecticide spikes recently, then the active insecticide in those spikes is probably imidacloprid. Imidacloprid is a mixed bag when it comes to safety. It’s not nealy as toxic as disulfoton, but it’s not non-toxic. It has been banned in Europe for a variety of reasons, the most important of which seems to be that it was implicated in the collapse of bee hives (imidacloprid is systemic insecticide so it will get into a plants pollen where honey bees could eat it). At this point it hasn’t been ruled out as having something to do with hive collapse here in the states — though if it does have a role it does not seem to act alone. It can also affect other beneficial insects who feed on pollen. Additionally, it has been known to control some pests while allowing mites to go crazy — in fact, it may even increase the rate of mite egg laying.
But imidacloprid is an effective insecticide which works against a wide range of insects which you that you might find on your plants. It is much safer than many of the older systemic insecticides, and it isn’t readily translocated to fruits (a problem that many people are concerned about with systemic insecticides is the movement of these insecticides into the fruit itself where it can’t be washed off — Imidacloprid is translocated to fruits –just not that much — it moves in the xylem and fruit takes up mostly phloem).
So these spikes are one of those things that I’m wary of. Not to say you shouldn’t use them, but be aware of what they are and what they could do before you buy them.