How To Stop Powdery Mildew

powdery mildew

My winter squash has what Mud Baron once described as “jock itch for plants:” powdery mildew. I’ve tried all kinds of notions and potions in the past, but this year I decided to see what the science says about powdery mildew. Our climate where I live in Los Angeles is, unfortunately, ideal for producing this vexing fungus.

IPM
Let’s begin with some condensed advice from UC Davis’ Integrated Pest Management page:

Preventative measures:

  • grow resistant varieties
  • find a sunnier spot for the vegetable garden
  • back off on nitrogen

Non-chemical approaches

  • sprinkle plants with water mid morning–add soap for more effectiveness
  • remove infected leaves promptly and dispose of them

Fungicides:

  • apply horticultural oil, neem oil or jojoba oil if the temperature is under 90° F. Do not apply any of these oils if you have used sulfur.

DIY Options
For home remedies I turned to advice from Washington State University horticulturalist Linda Chalker-Scott.

How about milk, widely touted as a powdery mildew treatment? According to Chalker-Scott the answer is yes it might work, but you may need to apply milk before powdery mildew appears. And the studies were done with whole milk, so the effectiveness of other kinds of milk have not been tested. Milk has not worked for me in the past, probably because I applied it too late.

How about baking soda? Chalker-Scott is skeptical. Baking soda has never worked for me.

Compost tea? I hate to bring it up as the topic is insanely controversial. I discovered a tempest in a compost tea pot when I tried to write a non-partisan magazine article about it. Let’s just say I ended up leaning towards the skeptical side when I looked at the evidence. Let me know if you think I’m wrong on this, especially if you can leave a link to a peer reviewed study.

Conclusions
What has definitely worked for me in the past is seeking out resistant varieties. I wasn’t smart enough to remember this fact so I’m going to try the soapy water approach and step up to something stronger if I have to. Part of my problem might also be too much nitrogen–my infected squash is in our straw bale garden and I had to apply a lot of blood meal to get it going. More sun would also help but that would involve cutting down a very large tree. I’ll update this post later in the season.

Let’s hear from you . . .
What powdery mildew treatment have you tried and how did it work? Leave a comment and join the conversation!

And I put the question out on the Root Simple twitter feed and got a few divergent opinions:

Christopher Kennedy ‏@ckpfunk Bonide’s Copper Fungicide for organic gardening. I spray every 14 days this time of year instead of every other w/ baking soda.

Alec ‏@Alec I’ve tried horsetail tea, sea-crop, baking soda, compost tea, and neem oil on mildew, but none compare to milk.

Alissa Walker ‏@gelatobaby I just sprayed with a baking soda solution seems to have done the trick so far. And removed all damaged leaves.

Alex Mitchell ‏@alexmitchelleg give the plants some air, water the ground not the leaves. Could spray diluted milk with water on leaves – never worked for me

Hens in the Orchard for Pest Control

hensinorchard

Photo: hencam.com

Author Terry Golson, who blogs at HenCam.com, sent along a great pest control tip in response to our thrip post–chickens, of course!

Chickens and orchards go together like gin and tonic. The hens take care of pests, clean up rotten fruit, add nitrogen to the soil and the canopy of the orchard protects the hens from hawks and heat. Plus you get eggs and meat. Permaculture in action.

The 1920s era photo you see above comes from one of Terry’s posts, Chickens in Orchards.

How to Deal With Thrips on Stone Fruit

thrip damage on nectarine

Research hint: when you have a pest problem on an edible plant, Google the name of the plant and “UC Davis.” What comes up is UC Davis’ handy Integrated Pest Management info sheets, evidenced based information on all kinds of problems. This is how I figured out that a small insect called the western flower thrip (Frankliniella occidentalis), was noshing on our nectarines.

Thrips damage the fruit when it is small. The scars enlarge as the fruit matures.

How do you manage thrips? UC Davis notes:

Western flower thrips overwinter as adults in weeds, grasses, alfalfa, and other hosts, either in the orchard floor or nearby. In early spring, if overwintering sites are disturbed or dry up, thrips migrate to flowering trees and plants and deposit eggs in the tender portions of the host plant, e.g. shoots, buds, and flower parts.

Thrips are often attracted to weeds blooming on the orchard floor. To prevent driving thrips into the trees, do not disc the cover crop when trees are in bloom. Open, weedy land adjacent to orchards should be disced as early as possible to prevent thrips development and migration of adults into orchards.

It was an exceptionally dry year which may have contributed to our thrip problem.  And perhaps some mulch and weeding around the base of the tree is in order. UC Davis goes on to suggest monitoring methods as well as organic controls if that’s your cup of tea.

The scarred fruit gets rotten on the tree and is unappetizing. We did get some unblemished fruit, but there was enough of a thrip problem to warrant monitoring next year.

Did you have thrip problems this season?

Hornworm meets alien!

So much better than that pointless Prometheus movie, is this glimpse into the kind of parasitism Hollywood just can’t match. In this Purdue Extension Entomology Service produced video, you’ll see a hornworm devour a tomato and then fall prey–Alien-style–to a species of parasitic wasp (Cotesia congregata). Not only do these parasitic wasps devour their host but in order to overcome the caterpillar’s defenses, mama wasp injects a virus before laying her eggs.

How do you create habitat for Cotesia congregata? Adults feed on nectar producing plants and, of course, you need to make sure you keep a few hornworms on hand!

Thanks to Jeff Spurrier for posting this video in Facebook.

How to Keep Squirrels and Birds From Eating Your Fruit

Photo by Noel Ramos.

Got a tip from Noel Ramos a.k.a. Florida Green Man on how to deal with those pesky squirrels and birds in your fruit orchard. Noel says:

I use those clear plastic fruit containers that are used for packing strawberries and grapes. I personally don’t buy fruit in these containers but I asked some neighbors and friends to save them for me and in a short time amassed a large collection. They snap shut over most fruit like these mangos and this helps to control fruit damage. Since they have vent holes, they don’t collect water inside. They can be washed and stored and are durable enough to last several seasons. After they serve their duty, they can be put in the recycling bin.

Noel is the person who sent the picture of all the winter fruit he grows in Florida that we put on the blog on Sunday. Judging from that picture he’s got a handle on critters issues. Thanks Noel!

Skunks, are they edible?

Skunk issues in the garden this winter have led to murderous thoughts. Those thoughts, in turn, caused an intemperate Google search which turned up the following gem from the March 1959 issue of Boy’s Life:

Incidentally, skunks are edible. The Indians ate skunk and so has many a trapper. I tried it, rolling pieces of cleanly-skinned carcass in flour and browning and steaming them in a skillet. The meat is light in color and well flavored. It is better than raccoon or opossum, but a skunk is bony and not as well padded with meat as a rabbit.

Not that I’m considering this yet. Somehow the thought of a locally sourced Los Angeles skunk is particularly unappetizing. And a reader mentioned that they kept a skunk as a pet. But I am curious to hear if any of you have tried skunk, raccoon or possum. Will we see any of these locally harvested meats on the menus of hip local gastropubs?

Butterfly Barrier Failure

So my idea about using 1/2 inch bird netting as a cabbage leaf worm butterfly barrier? Failure. Above is the photographic evidence–a butterfly caught within the netting.

So two alternatives:

  • Floating row cover (inconvenient and too warm for our climate)
  • More biodiversity in the garden

I’m liking the biodiversity option the best. Planting a bunch of brassicas is like opening an all you can eat buffet for cabbage leaf worms. Our backyard has more biodiversity and fewer problems with pests. I used better (homemade) compost  in the raised beds in the backyard, thus the soil in these beds also has greater microbial biodiversity

Bird Netting as a Cabbage Leaf Caterpillar Barrier

UPDATE: This idea is a complete failure–see the ugly details here.

Last month I sang the praises of floating row cover as an insect barrier. The only problem is that floating row cover retains heat, and so when our fall and winter days turn hot, as they so often do, it gets way too hot and humid inside the “tent.” So as Marshall McLuhan was fond of saying, “If you don’t like that idea, I’ve got others.” Specifically, bird netting.

I’ve got an untested theory that bird netting is enough to keep out the white butterflies that give birth to the dreaded cabbage leaf caterpillar, the only serious pest for us at this time of year. So far the bird netting seems to be working. I’ll note that it would be important to keep the leaves of plants well away from the netting so that butterflies can’t lay eggs through it. The best way to do this is by planting arches of wire or tubing over your garden bed, and stretching the cover material over those arches– like a covered wagon.

Netting has advantages over row cover: you can see and water through it and it’s more readily available.

I’m curious what you, our dear readers, think of the idea?

  • Mrs. Homegrown chimes in:  I’ll add that in the past readers have said they use tulle material as an insect barrier– you know, the stuff used to make tutus.

A Question About Gophers

Pocket gopher, courtesy of Wikipedia

We’re putting together a short vegetable gardening pamphlet and could use some advice, specifically about gophers. Thankfully, we don’t have any experience dealing with them. Something about our neighborhood, either the lead in the soil or the police helicopters, seems to have made gophers extinct here.

Standard advice when planting a tree or installing a raised bed in gopher infested areas is to use galvanized hardware cloth or gopher wire as an underground barrier. We even mentioned this in our first book. The main problem I have with this advice is that the galvanized metal used for hardware cloth and gopher wire leaches significant amounts of zinc as it breaks down. Zinc, in high quantities, is toxic to plants. And, when using cages for trees, I’d worry that the cages would not break down soon enough, causing the roots to circle.

Plastic, I’m fairly certain, would not work as the gophers would chew through it. And stainless steel is really expensive. Yes, you can trap gophers, and I’ll include info on that. But does anyone know of an alternative material for use as an underground gopher barrier? Extra points for pointing to a peer reviewed study.

Note: We just learned a new fact: “gopher” is a generic term that encompasses a few different critters. In other words, your gopher may not be my gopher. There are pocket gophers and a variety of ground squirrels who get called gophers. All are pesky. But the pocket gopher is sometimes called the “true gopher.”