Where the Bad Bugs Spend the Winter

Looking to build a winter resort for many of the bad bugs that inhabit your garden during the growing season? It's easy! 

Don't clean up any fallen leaves, branches or fruit beneath the infected plants. The aphids, whiteflies, scale and codling moth...especially the codling moth, will thank you.

So, if you want more sticky honeydew on your driveway, curled, deformed leaves and lots more holey fruit in 2011, just ignore this mess now.

Aphids!

A morning stroll through the garden is always revealing. The low angle of the sun highlights plant features that you might miss later in the day: the intricately beautiful circular web of the orb spider; ripened fruit, ready for picking, reflected in the morning light; and, of course, that behemoth zucchini you missed last night while collecting vegetables for dinner.

California Buckeye 46 Heirloom Bush Beans

That early walk can also highlight glistening leaves on your vegetable plants. A closer look may show that it is not the morning dew. It's a "dew" of a different kind, shimmering in the sun: honeydew, the sticky secretions of that ubiquitous bad bug, the aphid. 

Turn over that leaf, and voila! There's a colony of aphids, busily sucking the life out of your plant, curling and yellowing the young foliage.

What's a gardener to do?

Predatory Aphid Fly Larva

First of all, take a closer look. There may be other critters on that leaf, the garden good guys: natural enemies such as lady beetles, lacewings, syrphid fly larvae and predatory aphid fly larvae. It's the larval stage of these beneficial insects that do the most good. 

Syrphid Fly Larva (lower left)

Syrphid fly larvae, for example, move along plant surfaces, lifting their heads to grope for prey, seizing them and sucking them dry and discarding the skins. A single syrphid larva can consume hundreds of aphids in a month.

Parasitized aphids

Look for the mummified skins of parasitized aphids, where small, harmless (to you) parasitic wasps have laid their eggs which then hatch...inside the aphid, and crawl out!  

Look for disease-killed aphids as well: they may appear off-color, bloated, or flattened. Substantial numbers of any of these natural control factors can mean that the aphid population may be reduced rapidly without the need for treatment. 

If you see these garden good guys at work on the aphids, resist the temptation to spray broad-spectrum pesticides (organophosphates, carbamates, and pyrethroids). These kill natural enemy species as well as aphids. And guess whose population builds up more rapidly after such an assault? Aphids, which are born pregnant! Natural enemy populations do not appear in significant numbers until aphids begin to be numerous. Another reason not to use broad-spectrum pesticides: aphids can develop a resistance to those products. Mother Nature bats last!

The weather is your friend, as well. Populations of many aphid species are reduced by summer heat in the Central Valley and desert areas.

Aphids on a rose bud in spring

Check the other plants, as well, especially those on the upwind side of the garden, a favorite location for aphids. One tell-tale sign of aphids: the presence of ants, crawling up and down the plants. Ants herd the aphids and defend them from natural predators, in order to harvest the honeydew secretions for the ant colony. Control the ants with ant baits, and you can control the aphid population, too.

What If You See Aphids, But None of the Garden Good Guys?

My favorite way to reduce aphid populations on plants is to knock them off with a strong spray of water from the garden hose. Most dislodged aphids will not be able to return to the plant, and their honeydew will be washed off as well. Using water sprays early in the day allows plants to dry off rapidly in the sun and be less susceptible to fungal diseases. I do this two or three times a week on plants that the aphids find attractive.

Insecticidal soaps and light, horticultural oils (such as Neem oil) will kill aphids on contact. But soaps and oils will kill any beneficial insect it contacts, as well. Still, because soaps and oils have no residual action, any migrating beneficials will not be effected. Remember, too, that spraying soaps or oils on a hot day (90 and above) may damage your plants. Test a small portion of the plant with such sprays first.

Stop Aphids Before They Start: Tips from the UC Davis Integrated Pest Management Website

Before planting vegetables, check surrounding areas for sources of aphids and remove them. Aphids often build up on weeds such as sowthistle and mustards, moving onto crop seedlings after they emerge. Check transplants for aphids and remove them before planting.

Where aphid populations are localized on a few curled leaves or new shoots, the best control may be to prune these areas out and dispose of them. In large trees, some aphids thrive in the dense inner canopy; pruning these areas out can make the habitat less suitable.

On a newly planted vegetable garden, covering the seedlings with row covers can thwart the arrival of aphids.

High levels of nitrogen fertilizer favor aphid reproduction. Never use more nitrogen than necessary.  Apply it in small portions throughout the season rather than all at once. Most organic fertilizers can be classified as low level nitrogen products as compared to synthetically manufactured fertilizers.

Another effective aphid control method: snip off heavily infected branches and leaves, and put them in the trash or compost pile (if it is a hot compost pile!).

Aphids will always be with us. But there are plenty of garden good guys out there willing to help you in the battle...if you give them a fighting chance.

Tomato Troubleshooter: 2010 Update

Tomatoes - and tomato plant problems - abound this time of year. And 2010 is turning out to be an especially vexing year for tomato growers here in California, due to our cool, wet spring. And now that the summer heat has returned, many tomato problems have returned to the forefront of gardeners' attention. 

Good sources of information to help you solve your tomato travails are the books from the University of California Division of Agriculture and Natural Resources, "Pests of the Garden and Small Farm" by Mary Louise Flint and "The California Master Gardener Handbook," edited by Dennis Pittenger.

These books take an integrated pest management approach to solving plant woes. Instead of first reaching for harsh chemical controls, the books suggest adopting cultural, physical, mechanical and less toxic methods to solve the problems. Some of these solutions border on common sense, such as not planting tomatoes in too much shade; ripping out and destroying problem plants; or, trapping snails or earwigs at night beneath boards, then destroying them the following morning. 

Here are a few of the tomato problems you've been asking about this year, along with possible solutions, that can be found in greater detail in those publications:

Sunscald

Symptoms: Tomato fruit turns light brown and leathery, on side exposed to sun. 

Possible culprit: Sunscald (sunburn). 

Solution: Don't prune leaf cover from plant. Keep plant vigorously growing to produce more leaves.

SOLAR YELLOWING. According to the  UC Davis, Vegetable Research and Information Center , the reason for the yellow or yellow-orange color, rather than the normal red, is that the red pigment (lycopene) fails to form above 86 degrees (F). This phenomenon was first described by researchers in 1952 and was later confirmed by others. When lycopene fails to form, only carotenes remain for fruit color. An orangey-red color results. In production areas where temperatures do not exceed 85 degrees (F), much higher red color develops.

TOMATO FRUIT CRACKING. Radial cracking occurs during rainy periods, when rains follow long dry periods. Fruit exposed to the sun may also develop cracks. Maintain a uniform water supply through the use of drip irrigation or mulches. A full leaf canopy will also help protect fruit from the sun and reduce cracking.
 
Tomato Hornworm or Tobacco Hornworm
Symptoms: Tomato leaves eaten, areas of fruit eaten, black, pellet-like droppings on and below plant.  

Possible culprit: Tomato hornworm. 

Solution: Hand pick in evening or morning. Use sprays that contain Bacillus thuringiensis, a less toxic microbial pesticide, to control young hornworms.

 

 Blossom End Rot

Symptoms: Tomatoes are brown or black on the bottom end. 

Possible culprit: Blossom end rot. Due to a calcium imbalance, brought on by cycles of too much or too little water; other factors that may contribute to blossom end rot include improper soil pH (tomatoes prefer soil in a range of 6.0-7.0) and too much nitrogen fertilizer.

Solution: Maintain even soil moisture. Avoid varieties most prone to it.

Root Knot Nematodes

Symptoms: Poor vigor, reduced yields, tomato leaves turn brown from the bottom up. Swellings on the roots. 

Possible culprit: Root knot nematodes. 

Solution: Plant resistant varieties, labeled "VFN". Rotate crops. Solarize soil. Add compost.

 

Root Rot

Symptoms: Tomato plants grow slowly and wilt. Roots have water-soaked areas that turn brown and dry up. 

Possible culprit: Phytophthora root rot, common in overwatered clay soils. 

Solution: Avoid heavy watering for long periods. Water more frequently for shorter periods. Pull out and discard plant if problem persists.

Fusarium Wilt

Symptoms: Tomato plants turn yellow on one side, spreads to rest of plant. Inside of main stem at base is dark red (stem on right) instead of a healthy ivory color (stem on left). 

Possible culprit: Fusarium wilt. 

Solution: Plant resistant varieties, labeled "VFN". Rotate crops. Solarize soil. Remove old plants.

 

Verticillium Wilt

Symptoms: Older tomato leaves yellow, beginning between main veins. Internal stem is slightly tan colored, in small patches. 

Possible culprit: Verticillium wilt. 

Solution: Plant resistant varieties, labeled "VFN". Rotate crops. Solarize soil. Remove old plants.
 

RAIN-RELATED TOMATO PROBLEMS:

BACTERIAL SPECK: Hits during rain or overhead irrigation early in the season, during cool weather. Retards growth, reduces yields up to 25%, fruit spots, leaf spots. Leaf spots are near the edge of the leaf, dark brown with a yellow ring. Can spread throughout the leaf margin area. Common in cool coastal areas of CA. Solution: plant later in the season; avoid overhead watering.

BLACK MOLD: More common in the late season, when rain or free water affects ripening fruit. Can be cosmetic, or cause deep lesions. Pick fruit as it ripens; keep fruit surrounded by leaf canopy.

 

LATE BLIGHT: Develops during spring rain or overhead irrigation when air temperatures are near 70. The fungus overwinters on nearby areas where potatoes or tomatoes may have been planted. Purple-brown areas on leaves, turn to brown. Fruit may brown, but stays firm. Avoid sprinkler irrigation in cooler weather, especially if potatoes are nearby. Do not use sprinklers on bush-type tomatoes that have developed a dense canopy. Clean up and discard crops after harvest.

Tomato Cracking
  Can be rain or sun related. Maintain a uniform water supply through the use of drip irrigation or mulches. A full leaf canopy will also help protect fruit from the sun and reduce cracking.

Other problems that may be attacking your tomatoes this summer include whiteflies (control with insecticidal soap), aphids (ditto), powdery mildew (give plants full sun, regular watering and avoid excess fertilizer; organic vegetable fertilizers are a better choice), tomato russet mites (don't plant tomatoes near petunias or potatoes) as well as cosmetic tomato problems such as cat facing (puckering of fruit caused by cool weather when plant bloomed) and concentric circles near the stem (due to sudden, rapid growth).