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okiedawn1

Preventing/Controlling Spider Mites

Okiedawn OK Zone 7
16 years ago

Sheri and I discussed spider mites on a thread relating to a different topic, and I thought I would mention them here in their own thread as they pose such a threat to home gardeners.

Spider mites are tiny sucking insects that attack all kinds of plants, including veggies and herbs, flowers, shrubs and trees. They are at their absolute worst during the hottest part of the summer and can damage plants enough to kill them. They are related to arachnids like spiders and scorpions, not insects, so a standard insecticide will not kill them, although a miticide might (or at least should) but usually doesn't!

Spider mites appear as tiny dots (about the size of a period), usually on the underside of foliage. The most common ones I see are the red ones, but there are others as well. If you think a plant has spider mites but are not sure, hold a white sheet of paper underneath the leaves of the plant and tap or shake the leaves. If tiny little dots fall onto the paper and begin crawling around, they are most likely spider mites. Other symptoms of spider mites include a tannish to yellowish mottling of the foliage and tiny, tiny webs on the plant foliage.

MY BACKGROUND WITH SPIDER MITES: When I was a kid, it was common for my dad and other home gardeners in our town (Fort Worth, TX) to experience HUGE amounts of damage from spider mites. As the summer heat worsened, usually beginning in July, the red spider mites appeared, multiplied and killed many garden plants, including all the tomato plants. I remember that it didn't seem to matter what the gardeners did (including spraying the garden with DDT, which was common back then).....the spider mites would win.

Naturally, after watching dad and his friends battle spider mites my entire life, I had an unnaturally strong "fear" of spider mites.

As a young woman with a home, family and "home vegetable garden" of my own when I was in my 20s, I dreaded the annual appearance of spider mites. I wasn't completely organic then, so did try to fight the mites using conventional methods, and failed.

I began to plant fall tomatoes partly as a way to guarantee we'd have some tomatoes from the "new" fall plants after the spider mites killed all the "old" plants. It is worth noting that in June and July the mites attacked plants that had been planted in the spring and were, in fact, in glorious full production, loaded with ripening tomatoes. They did not, however, tend to attack rather recently-planted fall tomatoes. (More on that later.)

THE USE OF DICOFOL: At one point in my childhood, Kelthane (a miticide whose primary ingredient was Dicofol) was the go-to treatment for spider mites. IF you started early enough (very early) and sprayed often enough, the Kelthane MIGHT keep the spider mites to a manageable level. At some point, though, it seems like Kelthane (Dicofol) was either removed from the market or simply disappeared. I think it was in the 1990s. It seems like Dicofol (often sold as Kelthane) reappeared on the market a few years ago.

Have I ever used a Dicofol product to try to control or eradicate red spider mites? Yes. We used it two consecutive years in the mid to late-1980s. Did it work? No. Were we concerned about using it? Yes. Have we used it since? No.

If you are not familiar with Dicofol, I'll just mention a little about it. It was once used as the "go to" or "sure thing" product for the control of spider mites. At one point, it seemed very effective. However, as occurs with MANY pesticides, overuse seemed to cause it to lose its' effectiveness. Often this occurs when targeted pests develop resistance to a pesticide, although I am not sure if that is what happened in this instance.

As far as I know, Dicofol is still in use, especially in commercial citrus and cotton crops in the U.S.

Dicofol (I learned this AFTER we used it) is basically derived from DDT although it is not considered as toxic. However, it is considered slightly toxic to birds, highly toxic to aquatic organisms and is not known to be toxic to bees. It is classified as a Class III human carcinogen.

Humans who are exposed to Dicofol can have serious problems, including: dizziness, nausea, vomiting, damage to the central nervous system, conjuctivitis (if eye exposure occurs), skin irritation or rash, coma, convulsions and death. It is a nerve poison.

Also, and this is especially important for pregnant women, a study by the California Dept. of Agriculture (results reported in 2007) found that women exposed to Dicofol during the first 8 weeks of pregnancy (even if they only lived "near" farms that used it) were several times more likely to give birth to children with autism.

For these reasons, I wouldn't user Dicoful nowadays under any condition. What's a gardener to do, then, if spider mites are a problem?

BATTLING SPIDER MITES TODAY: When we moved to Oklahoma in 1999, I was determined to be 100% organic. Have I succeeded in that? No. But I am about 95% organic and that is not bad.

During our first two gardening seasons here, we had horrible spider mite problems. I believed then (and still do) that the problem was mostly that our new garden beds were deficient in something they needed. I worked hard to improve the soil by continually incorporating all the organic material I could. Every year, therefore, our soil has gotten better and better. In what MIGHT be a related development, our spider mite problem has decreased every year.

Healthy soil produces healthy plants. Healthy plants are more resistant (though not totally immune) to all pests, including spider mites.

The first 2 years we were here, I KNEW we had soil fertility problems so I fed (and, OK, probably OVERFED) my veggie garden and flowers with Miracle Grow and similar products. I had TONS of insect problems. Research at that point let me to a belief commonly held by many organic gardeners that plants which are chemically fed/overfed have more pest problems. I found this to be true. Once I stopped relying on chemical fertilizers and started using only organic fertilizers, my pest problems decreased. My spider mite problem now is probably only about 5% of what it was when I used miticides. I discontinued the use of chemical fertilizers except under the MOST EXTREME conditions. Last year, because I knew the heavy rains had leached much of the nutrients out of our soil (knew it because the plants showed syptoms of nutritional deficiencies), I did feed my plants once or twice with Miracle Grow to help them grow. It worked. I didn't overfeed them, though, and I didn't have much of an insect problem.

Having healthy soil and healthy plants goes a long way towards keeping spider mites from devastating your warm-season veggie crops and ornamentals, but you have to do more.

Stressed plants are more susceptible to spider mites, so good soil drainage is important (soil that is too wet is a huge plant stressor). Keeping your plants evenly moist through adequate irrigation and mulching is important too.

Spider mites WILL appear in your garden at some point. When they do, all you need is to have a few tricks up your sleeve. Here's some of my favorites.

1. Spray leaves, ESPECIALLY the underside, with a blast of water. It will knock off a lot of the spider mites.

2. Spray you plants weekly with an organic foliar spray like liquid seaweed or compost tea or Garrett Juice. It does make a difference.

3. Encourage beneficial insects. Lots of insects eat mites and mite eggs, so the more beneficial insects you have, the less of a problem you'll have with pest bugs. Ladybug beetles, green lacewings, and parastic wasps all are very helpful in the garden. If you don't have a naturally occurring population of these, you can buy them and release them. I stay away from praying mantids, though, as they will eat the beneficial insects too.

4. Plant flowers and herbs that attract and feed beneficials. Many of the plants that have very tiny flowers are attractive to beneficial insects, including yarrow, carrots in their second year when they flower), tansy, feverfew, alyssum, Queen Anne's Lace (wild carrot) and many of the clovers attract beneficials. You can buy seed mixes that are sold as "good bug attractors" to help attract and keep these beneficial insects in your garden.

5. You can buy, mix and use a "bug food" that helps feed the beneficials too.

6. You can plant a "trap crop" of marigolds to attract the spider mites. Once the marigolds are covered with spider mites (but before the mites begin to move to your tomatoes or other veggies in large numbers), pull up and completely dispose of the marigolds. I either burn them, or put them in a sealed garbage bag and dispose of them with the household garbage.

7. If you have an incredibly extreme infestation of spider mites, and money is no object, you can purchase a species of spider mites that actually eat other spider mites. Arbico is one of many companies that sells these, but they are expensive and I wouldn't spend that kind of money on an infestation in a home garden. If, however, you raise crops to sell, or have spider mites in your greenhouse, the expense could be justified.

Nowadays, I employ all the above methods--avoiding chemicals, keeping plant stress to a minimum, encouraging beneficials and the use of trap crops, to keep spider mites to a minimum. Most years I don't see any at all, or at least not very many. If my dad were still here, I think that he'd be amazed.

And, incidentally, what works to reduce the population of pests like spider mites, generally works for most other garden pests. Healthy organic soil is the key, but it does take time. My spider mite problem went away gradually as the soil and plants got healthier and healthier.

If any of you have any more info to offer on how you combat spider mites, I'd love for you to share it here with us.

Dawn

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