Squashing the Whitefly Invasion


It must be August, because my squash leaves are starting to look pretty sad in places. I noticed the beginnings of a whitefly problem a few nights ago and tested a new do-it-yourself spray on a group of leaves. Two days later, the test leaves looked great, but the rest of the squash patch was starting to show more serious signs of infestation. Today I sprayed the top and bottom surface of every leaf I could find with evidence of whiteflies and then some. I’ll track the results in a few more days and update things here.

The varieties of squash in the patch are:

‘Vegetable Spaghetti’ (C. pepo)
‘Candy Roaster Melon’ squash (C. maxima)
‘Upper Ground Sweet Potato’ (C. moschata)
and ‘Jim’s Butternut’ (C. moschata)

This last one was saved from ‘Waltham Butternut’ many years ago and kept going by a neighbor. It grew 25 foot vines with 10 fruit on a single vine in 2012. If some of that productivity crosses into my ‘Upper Ground Sweet Potato’ seeds for next year, maybe it will be a good thing!

The ‘Spaghetti’ squash is suffering the most from the whiteflies, though I first noticed it on the ‘Upper Ground Sweet Potato’ leaves. Maybe I didn’t notice it on the ‘Spaghetti’ squash because it’s harder to get to their part of the patch? The ‘Candy Roaster Melon’ is clearly the least affected. It’s much slower growing than the other varieties and is just now, in August, starting to flower. I have yet to find any research on differing vulnerability to whitefly across squash species, so the differences I see may have other causes. It is certainly too early to say that C. pepo is more likely to suffer whitefly infestation and C. maxim is more likely to fend it off—but that’s a theory that might turn out to be worth testing.

Homemade Whitefly SprayThe spray that I made started with 1 Tsp of Dawn Advanced Power liquid dishwashing soap mixed into 1 cup of vegetable oil. This makes a concentrate that you then mix with water in your sprayer. Add 1 1/2 tsp of the concentrate for each cup of water you add into the sprayer. I mixed 3 cups worth at a time in my regular household spray bottle. Next time I will seriously consider a backpack sprayer. In order to control whitefly everything I have read emphasizes the need to spray both the tops and the underside of the leaves. This can quickly become a tedious and finger-numbing project with your average spray bottle.

Next year I will plan ahead. The U.C. Davis Integrated Pest Management site says, “Several wasps, including species in the Encarsia and Eretmocerus genera, parasitize whiteflies. Whitefly nymphs are also preyed upon by bigeyed bugs, lacewing larvae, and lady beetles.” Buglogical has additional suggestions to try. If I manage to establish populations of these good bugs in my garden before August next year, maybe we won’t see the whiteflies at all.

Do you have a whitefly cure that works well in your garden? Please share it in the comments. And if you have tried something that didn’t work, I’d like to hear about that as well.

Updated August 31, 2013

The spray has had mixed results. The plants are still going, and new fruit is even being set, but there is noticeable damage from this pest on a number of leaves. Below is an example from the ‘Butternut’ patch.

Butternut Squash Leaves

Butternut Squash leaves treated with homemade whitefly deterrent.

The growing tips look healthy and you can see at least one young squash has been set during the Whitefly/Mildew invasion. But a number of leaves may have been too damaged to recover. And the nastiness is clearly spreading again.

Spaghetti Squash Leaves with Whitefly or Mildew

Both sets of leaves you see here are from the same Spaghetti Squash, one clearly much more affected than the other.

Only the few five-fingered leaves you see here are not from this plant. Seeing these leaves so close together, clearly growing in the same conditions, makes me wonder about the variability for disease resistance in these squash.

12 thoughts on “Squashing the Whitefly Invasion

  1. Perfect timing–I am having a white fly invasion on my cole crops, and I am also using soap spray (sans oil), but no miraculous results yet. However, I agree with Laurie–it looks like powdery mildew, which I am also suffering an invasion of! It could be both of course. I read somewhere that hot dry weather is as bad if not worse for pm–something about spore dispersal. My squash seems to still be producing for now though, it is just hideous.

  2. The dish soap is an emulsifier(or wetting agent) and allows the vegetable oil to mix with water. When you spray the leaves with this mix diluted in water, it leaves a thin layer of oil (lipids) on the surface of the plant(kind of like skin lotion). This added protection for the plant is enhanced with an herbal extract like rosemary, peppermint, sage, thyme, clove or chili powder that have been shown to deter insects.

    • Thanks, Dan. I happen to have a lot of peppermint oil on hand, so maybe I will do another test comparison adding some of that in. What about a foliar fish emulsion or compost tea now, to feed the leaves and hopefully fortify them after the bugs have been sucking at them? I wonder if that would help?

      • I would recommend the compost tea over a fish emulsion. The beneficial microbes activated in a compost tea will help compete with the destructive mildew as well as feeding some micronutrients into the foliage. If you can add kelp to your tea, it will probably do the most, being rich in micros. The fish emulsion is best added to the root area as it works in concert with the soil microbes. On the leaves the fish proteins and fats will not only block light absorption but might also feed destructive microbes.

        As far as foliar feeding goes, natural soaps (Castille/Veggie based) are a lot gentler on plants than petroleum based (Dawn) and don’t leave a weird taste. Neem oil is one of the best to use mixed with soap because the phytochemical Azadirachtin in Neem repels insects and fungus. The herb Thyme or Potassium Bicarbonate are both excellent for killing mildew.

        For killing whiteflies, they’re one of the hardest to eradicate. I’ve never seen ladybugs make enough of a difference to use them. Encarsia wasps work well but need to be started before the problem for them to maintain it, and they’re expensive long term to release. Using a Pyrethrin (Chrysanthemum phytochemical) spray will probably help most as it’s a strong insecticide and one of the safest for us. I hope this helps :-) -Nate

      • Nate, I made some compost tea and sprayed with it today. Some of the leaves are looking papery and starting to yellow, so I don’t have much hope for those, but maybe it will help the leaves that still look healthy and green do as much as possible for the plant. How long do you usually wait between compost tea foliar applications? A week or so?

  3. Sounds great! I haven’t had any problems in the garden, but the other farm had some in greenhouse. I used soapy water too…didn’t think to add the veggie oil…that probably helped it stick real good! Thanks for the tip!!

    • Thanks, Pam. U.C. Davis says we don’t get the same kind of whiteflies on squash here that are usually seen in greenhouses, so I don’t know if you need the oil or not. Did the soapy water help? Did it hurt anything you tried it on? I worry about how it affects other things in the soil. I’m always worried I’m going to hurt the “good” bugs when I start using something like this but it’s too early to give up on the squash crop. We’ve got almost 100 days left before frost.

    • Laurie, it’s been so hot and dry here all summer that mildew would surprise me. I’ll have to look for some good photos that compare the two problems and see what I can figure out. What’s the best way to tell? When I get up really close with the macro lens it certainly looks like larval somethings on the leaves, but I’m no expert in that area.

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