Post #G17: Garden update: Flying Yogis?

Posted on August 11, 2020

No, hovering cardinals.

Hovering cardinals, hoovering up sunflower seeds.

I thought that by the time my sunflowers put their heads down (left), at least some seed would be safe from the birds.



Guess again.




Briefly, here’s my garden update.  Details follow below.

  1. Squash vine borer.  Spinosad spray appears to have been almost 100% effective in preventing squash vine borer damage.  Lot of work, though.
  2. Powdery mildew.  I’m currently trying three sprays for powdery mildew on cucurbits:  mouthwash, milk, and “triple-threat” spray (horticultural oil-potassium soap-potassium bicarbonate).  This is after several prior fails documented in an earlier post.  Provisionally, the “triple threat” spray appears to be working.
  3. Cucumber beetles are still here.  I seem to have reached an equilibrium of finding and crushing around six per morning.  Bacterial wilt (spread by that beetle) has killed virtually all my cucumbers, and I am stubbornly replanting the same species for a fall crop.
  4. Regarding sunflowers:  I never knew that cardinals can (briefly) hover like hummingbirds.  What they lack in grace, they make up for in determination.  As long as the prize is black oil seed.
  5. Summer squash vines will run.  Mine are climbing out of their raised beds and down onto the lawn.  I now have some yellow squash set a good solid 8′ from the root of the plant.  Never had that happen to me before.
  6. Pumpkins.  Pumpkins everywhere.  If I can get the powdery mildew under control, I’m going to end up with my back yard being my own private pumpkin patch.  I harvested my first pie pumpkin a couple of days ago.

Details follow.

Squash vine borer (SVB).  At this point, I’ve had one bit of damage at the very tip of one zucchini that plausibly was due to a borer.  But there was no live borer there when I broke open the stem.  That plant continues to produce.

Given that I have a lot of cucurbits, and had a lot of SVB moths (daily sightings from 7/5/2020 to about 7/25/2020), I think my treatment was effective.  I sprayed 0.008% spinosad (from concentrate) onto the stems of my cucurbits, in the evening (to avoid bees), roughly every five days.

Could be luck.  But given the number of moths, and and number of stems, I’m leaning toward this being effective.  Without a controlled trial, there’s no way to know for sure.  And I didn’t feel like sacrificing half my cucurbits to science.

I learned two other things.

First, the SVB will lay eggs all up and down cucurbit stems, not just at the base.  And they’ll go after any cucurbit,  not just summer squash.  The very first SVB moth I observed was, in fact, ovipositing at the base of a zucchini.  But by the end of their three-week season, I observed SVB moths ovipositing pretty much everywhere, all the way out to the tips of the pumpkin vines.

I suspect that the SVB moth can tell when another SVB has laid eggs in an area.  So if you have a moth or two, sure, wrapping the bottoms of your summer squash stems may be adequate.  But if  you have enough moths visit, you’ll find that the later moths work on fresh areas of stem, and other plants.  And in the end, with enough moths, any stem on any cucurbit becomes a target, to some degree.

Second, there are pheremone lures/traps for SVB moths, but these are sold as monitoring devices, not as control devices.  I’m not sure why, but I think that may be because they only lure in the male moths.  Depending on mating habits, or maybe the size of your acreage, this may or may not reduce the number of eggs laid by female SVB moths.  In any case, I didn’t get around to testing those.

Powdery mildew.  Ah, the stuff I didn’t know about this disease, and wish I’d never had to learn.  An ounce of prevention is worth a pound of cure, because it’s really hard to get rid of.  See posts #G15 and #G16 for background. By far, the best and most helpful guide I found was this somewhat dry page from the University of California system.

Most commercial fungicide products are sold as protectants.  They’ll prevent spread, but they won’t cure an infected plant.  That ranges from very old techniques (sulfur, copper, bordeau mix) to modern chemicals that disrupt specific aspects of the powdery mildew life cycle.  Enough of the high-tech chemicals had enough risks (e.g., to aquatic life) that I decided that I wouldn’t use them anyway.  Not to try rescue $20 worth of pumpkins.

Similarly, most home remedies are exclusively or primarily billed as protectants.  That starts with baking-power solution, and plausibly includes hydrogen peroxide solution (described as having “some” ability to eradicate fungus).

So I did my research and came up with the three most promising things I could readily lay my hands on:   Milk, mouthwash, and (my) combination of three traditional items thought to have some eradicant ability, what I call “triple threat” spray.

Milk.  The research literature behind use of milk appears pretty good, but with a lot of questions.  In at least one controlled trial, milk spray (at varying concentration) was good at suppressing spread of powdery mildew on cucurbits.  At high concentration (40% milk, 60% water) it worked better than a commercial fungicide.  But how it works, what kind of milk to use (whole-fat or skim), and whether it is an effective eradicant all appear to be unknown.  In any case, this is one spray that should be applied in full sunlight.

Mouthwash.  I included this one only because it was vaguely plausible, and because I could find not a single shred of evidence.  Not even a testimonial from a gardener.  So this one had the feel of an urban legend, but … given that I own some, why not try it.

Triple-threat spray.  Based on the U Cal reference above, standard horticultural oil is billed as an eradicant, and standard light horticultural oil is better at it than 70% neem oil extract.  I also found a product sold as an eradicant that turned out to be “potassium salts of fatty acids”, that is, traditional soap made with potassium hydroxide instead of the more traditional lye (sodium hydroxide).   Dr. Bronner’s is also, famously, potassium-based, which is part of what makes it so effective on soft-bodied insects.  Finally, potassium bicarbonate is sold to farmers as a powdery mildew eradicant, and apparently has been for some decades.  Both the potassium-based soap and the potassium bicarbonate have a presumed mechanism of action of disrupting the cell walls of the mildew, and so killing it.

I looked up the dosages for the soap and potassium bicarbonate based on the commercial agricultural products.  And looked up the recommended dosage for the horticultural oil.  Rounded the numbers to keep below the maximum allowable concentrations, and in the end, came up with a simple recipe of one fluid ounce each of potassium bicarbonate, light horticultural oil, and Dr. Bronner’s soap, per gallon of water.  (The potassium bicarb is a solid, but the fluid ounce turns out to be just about the right weight of it, per gallon.)  That combines three substances that were reputed to have some ability to eradicate powdery mildew.

I sprayed down a small section of pumpkin vine yesterday.  One stretch of vine with what appeared to be equally mildewed leaves along it, divided roughly into thirds, one spray on each segment.

The patch with the triple-threat spray looks vastly better than the rest of it, today.  That might be an illusion.  And maybe this spray will end up killing the leaves. But this is the first time I’ve come back after spraying for mildew and said, huh, that certainly looks different.

Here’s a side-by-side close-up of a single leaf, yesterday versus today.  Note that the mildew has regressed from white to yellow on much of the upper half of the leaf.  Focus on the northeast quadrant of the leaf.  I can see the chlorophyll-deficient yellow portion of the leaf now in places where that was formerly hidden by the white mildew.  This may just be an illusion caused by residue of the spray (although the oil should have evaporated by now).  But that sure looks like it knocked the mildew back quite a bit.  As I said, first time that’s been completely obvious by eye.

By contrast, the milk appears to have done next-to-nothing.  That would make sense if it were primarily a protectant, not an eradicant.  (Or if it works far more slowly).  And the mouthwash was, to my surprise, somewhere in-between.  Again, vaguely by eye, it looked like the mildew was knocked back a bit on the portion sprayed with 25% mouthwash solution.  But nothing like the amount of reduction on the triple-threat section.

So, I don’t know which ingredient or ingredients in the “triple threat” spray are responsible for this.  But I don’t have to care, as long as it doesn’t harm the plants.  Plus, it looks like I can mix this up in concentrated form and spray via a hose-end metered sprayer.  That’s going to be a must-do, I think, given the large amount of leaf area I’m going to have to spray down.

Sunflowers and hovering cardinals.  Never would have believed this if I hadn’t seen it.  They can’t peck out the sunflower seeds once the heads have turned downward.  Instead, they perch on a leaf below, launch themselves at the underside of the head, hover, snatch some seeds, and fly off.  I’m going to try to catch it on video.  The upshot is that I had to go out and gather whatever seed I wanted to keep for re-planting.  Between the cardinals and the goldfinches, there isn’t going to be any sunflower seed left on the plants.

Here’s a YouTube video of a hovering cardinal.  I think they have to be fairly well motivated to spend the energy it must take to do that.

Cucumber beetles are still here.  Today I went 3/3 (kills/attempts), plucking them out of the squash blossoms with long-nosed pliers.  Yesterday was 6/6.  It doesn’t look like this method can eradicate them entirely, just keep them in check.

They are definitely mating, so it’s possible that they’ll now die back naturally, based on their life cycle.   At which point, we should have a couple of months without them, as their eggs hatch and their larvae pass through several life cycles in the soil.  Before they re-emerge as adults in the fall.  I’m going to dose my beds with beneficial nematodes, as these are reputed to kill the cucumber beetle larvae.  (The alternative is to drench the soil with spinosad to kill the larvae, but I think I’ve sprayed enough of that for one year.)

My cucumbers are nearly 100% dead from bacterial wilt.  Brought on by these bugs.  So I’d like to return the favor and kill as many of them and their offspring as possible.

Summer squash vines will run.  In the past, my summer squash were always fairly compact plants.  They stayed where I put them.  This year, I have several where the main vine has run feet and feet from the original root.  Maybe I let them get too much foliage, so they ran for sunlight.  Maybe the heat did it.  Hard to say.  The one pictured above escaped the raised bed entirely and is setting yellow squash in the middle of the lawn.  The vine is easily eight feet long at this point.  Never knew they’d do that.

Pumpkins.  I put in a bunch of pumpkins, in various places in my yard, because I read that they produce a lot of edible calories per square foot.  I figured they’d be an easy, hassle-free crop.  Hah.  I keep the SVB off them, I’m now going to try to keep the powdery mildew off of them.  And if that works, I’m going to have a lot of pumpkins, come this fall, everything from pie pumpkins (smaller than a soccer ball) to Connecticut field pumpkins (traditional jack-o-lantern pumpkins).  I’m looking forward to it.