Pests and Pesticides

We are frequently asked about how to best control unwanted garden pests and thought this article from the Institute of Food and Agricultural Services, Univ of Florida might be useful.

The best advice is to stay away from insecticides unless you see a problem. Pesticides that drip into our waterways cause fish kills and other environmental problems. I recommend that you use organic controls whenever you can. Insects build up resistance to pesticides, creating superbugs. Use the safest product possible and make sure you have the problem correctly identified so you will not use the wrong pesticide. Less usually is better than more. I have sprayed only twice on my property in the past 17 years for a localized problem.

General Suggestions:
Spray in the early morning or late evening when the temperature is below 85 degrees. Spraying when temperatures are over 85 degrees can burn leaves and cause leaf yellowing or leaf drop. Do not spray if it is windy as some sprays stain or could hurt adjacent plantings. Copper fungicide is an example as it can stain everything electric blue like your house or paving. Repeat treatment in 7-10 days to kill new pests hatching from eggs. Use a spreader sticker or a few drops of soap with your pesticide mix to help the spray adhere to the plant.

Clearly many of the most frequently asked questions regarding insects revolve around tomatoes, those succulent orbs of earthy delight. As versatile as they are delicious, they can be grown in pots on a patio or planted in the yard. One bite will convince you that, whatever their problems, they are worth the effort. From letters and samples sent or presented to me at plant clinics, I present the condensed guide to growing tomatoes.

They can drive you buggy! A woman has a small Baggie in her hand. Inside is a branch from a tomato plant. The leaves are green but oddly puckered.
“What’s wrong with my tomatoes?” she asks plaintively. The answer is aphids -small, soft-bodied insects that suck plant juices. The telltale sign is the twisted leaves. The remedy is a thorough spray with the garden hose or an application of insecticidal soap.

The next person carries the patient, or a small piece of it, in a plastic dish. Again, it’s a tomato plant. Yellow leaves, with small dark splotches. Hmmm. Could be blight or maybe leaf spot. Both are treatable, if not curable, with a copper sulfate spray or a weak solution of hydrogen peroxide.

But it could also be fusarium or verticillium wilt, in which case the prognosis is poor. The gardener should have used a disease - resistant variety.
You have to face it. Pests are the order of the day with tomatoes. Expect leaf damage, but don’t let it drive you crazy. Some insects, such as leafminer, will make the leaves look awful, but they will not affect fruit yields.

One of the reasons we grow our own food is to have some control over what chemicals go on it. It’s best to avoid heavy doses of pesticides. Use commercial insecticidal sprays as a last resort.

Beneficial insects are a good first line of defense. Ladybugs control aphids, mealybug, scale and other sucking insects. Praying mantis control larger insects such as grasshoppers, beetles and other chewing pests. Parasitic wasps lay eggs on caterpillars, such as tomato hornworm and other larvae. Give the good guys a few days to start working on the bad guys before you panic. Now, let’s get more specific.

Aphids

Aphids come in many colors, from rosy pink to gray to pale green and they attack almost anything. Some have wings; others don’t. If your plant is growing slowly, or if the leaves (especially the tender young ones) look twisted or puckery, check the underside for these little sap-sucking insects. Their sucking causes distorted foliage and poor growth. They may also spread tobacco mosaic virus, a disease fatal to tomatoes.

A strong spray of water will wash them off, but you will have to repeat the treatment often. You also can use a commercially prepared insecticidal soap, available at garden centers, to suffocate them. Or put a couple of tablespoons of hydrogen peroxide in a gallon of water and spray the plant regularly.

The good news? Aphids are a favorite food for ladybugs.

Stinkbug

An occasional problem on tomatoes and citrus, stinkbug is a shield-shaped bug about a half inch long. It can be green, black or brown and can leave a foul odor on your hands if it is handled.
Stinkbug punctures the fruit and sucks out the juices. The fruit will change color where the stinkbug feeds and leaves a toxin behind; a tomato will turn white or yellow in the affected areas.
The best control is to remove weedy areas where they hide close to the tomatoes. If you continue to have problems, dust the fruit with diatomaceous earth or spray with insecticidal soap.

Cutworm

Cutworm is a major problem for new tomato transplants. The caterpillar is about 1 to 2 inches long and is usually black or gray. Active only at night, they hide below the ground during the day. They chew new transplants off at the ground level and the plant topples over and dies.

The easiest solution is to put a “collar” around the transplant after it is set in the ground. You can use almost any material _ cardboard, empty vegetable cans with both ends removed or empty toilet paper tubes. Make sure the collar is pushed down about an inch into the soil and is at least 2 inches high

Tomato fruitworm

Tomato fruitworm is active in south Florida. The caterpillar is about an inch and a half long and can be green, pink or brown. It enters the tomato at the stem end and feeds on the fruit, making it worthless. Nature can take care of these pests because they are often parasitized by trichiogamma wasps and tachnid flies. Or you can dust the fruit with diatomaceous earth or Dipel.

Tomato hornworm

The tomato hornworm is a big guy _ more than 4 inches long- but its dark green color makes it difficult to see in foliage. It gets its name because of a horn at the rear end of its body. One or two of these fellas can eat an entire plant. Leaves may be chewed to the stem; occasionally fruit also will be consumed.

In most cases, they can be picked off by hand and dropped in a can of kerosene or ammonia. The best time to find them is at night using a flashlight, because they hide during the day.
One warning: If you find a hornworm or other caterpillar with small white sacks on its back, leave it alone. The sacks contain the larvae of a small wasp that preys on the hornworm and other caterpillars.

Blossom end rot

Blossom end rot is a common problem on tomatoes. One end of the fruit rots making it unuseable. A calcium deficiency is the cause of this disorder. Try spraying 2 times a week with 4 tablespoons of calicium chloride mixed in 3 gallons of water. Spray 1 quart per plant.

New Insect Pests:

Dr. Catharine Mannion, ornamental entomologist at the Tropical Research Station in Homestead, reported on some new insect pests to watch out for in Florida. They have all started in the Miami area.

• A new thrip has been discovered on pink tabebuia’s in Dade County in 2001. It feeds on the trees leaves causing leaf distortion, folded, and curled leaves that may be covered with galls. The insect is best controlled with systemic insecticides.
• The lac scale was discovered in 1999 and is globe shaped with a waxy covering. Lac scale can be light to dark reddish brown in color. It attacks new stems but not leaves. Oil products like Organocide should offer good control. This scale has been noted on wax myrtle, cocoplum, buttonwood, and sand live oak in the native plant group. Exotic black olive, and weeping fig are also affected.
• A Sri Lanka weevil has been found on lychee and mango trees in Dade County. This weevil has a wide host of plants that it will feed on. It could cause serious damage. Weevils chew foliage and roots.
• The strangest pest of all is a spider which does not prey on the plant itself. It makes heavy horizontal webs which can completely cover a plant cutting light off. The plant will eventually die from lack of light. The spider should be killed to stop nest building but it is important to have the spider properly identified before any spraying is done.
• The pink hibiscus mealybug is the latest pest to visit south Florida. It was identified on 2 hibiscus plants in Pembroke Pines. This bug can attack over 200 different plant species. It is spread by wind and ants. Florida Department of Agriculture staff are trying to eradicate the pest. If it escapes eradication a small Puerto Rican wasp offers hope for control. This mealybug was last seen in southern California in 1999 where it was eliminated. It has the potential to weaken and even kill some plants here.
• The Lobate Lac scale now is attacking 120 Florida plant species including 39 native species such as wax myrtle, cocoplum, buttonwood, strangler fig, myrsine, red bay, and wild coffee. Exotics like black olive, Indian laurel fig and Benjamin fig are also attacked as are edible fruit trees like mango, lychee, and starfruit.
• Ficus benjamina has been under recent attack with the lac scale whose voracious feeding turns the ficus leaves black with sooty mold.
• A new thrip is now attacking Ficus benjamina. The thrip curls and distorts the leaves and the pest has been found in Dade and Broward counties so far. The damage is similiar in appearance to the thrip that has attacked Ficus retusa foliage for years. Ortho Systemic Insecticide and Bayers Tree and Shrub insecticide will control this pest. Gore Nurseries, Bob Betz told me about this new insect pest.
• The gall or bud midge is a new pest attacking hibiscus blooms. The flower buds drop after this pest attacks. Thrips were the other pest attacking the buds causing bud drop. Ortho Systemic Insecticide will control this pest. Ortho Systemic Insecticide has a danger label so follow label directions exactly. A biological control offers the best long term cure but a soil drench of systemic Merit or Bayer’s Lawn and Garden Care will offer quick control. Follow label directions exactly. Remember that systemic insecticides will also poison the fruit so these products are not recommended for fruit trees.
• My ‘Knockout’ rose had pale stippled foliage and I decided to see what the problem was. The leaves on this otherwise healthy rose were almost white in color.
• It turned out that the problem was the Chilli thrip. This pest is particularly bad on the ‘Knockout’ rose. It can also affect many other plants with documented attacks on yeddo hawthorn, Viburnum suspensum, and Rhododendron species. It can attack many different plants. I treated the rose with Bayer’s Tree and Shrub Care soil drench and the problem cleared up within a few days. The old leaves dropped off and the new growth and flowers look good. This product should protect the plant for at least a year if label directions are followed.
• We were almost invaded recently by the giant harlequin beetle. This pest has the ability to kill mango and cashew trees by burrowing into the trunk and branches eventually killing the tree. This long horn beetle has big antennae which help to identify it. The bettle can also blemish fruit. Department of Agriculture plant inspectors found the pest walking on the deck of a freighter from Honduras. The beetle was captured and fortunately did not make it to our shores.

More New Insect Pests added 1-08

Red Palm Mites are the newest pest on palms in South Florida. These mites attack coconuts first but also feed on date and areca palms. They have been found on 32 different types of palms. Insecticidal soap or oils like Organocide offer control for homeowners. Merit should work for commercial applications. Damage would be most apparent in the dry season. Stippling is the initial appearance on foliage and eventually spots spread to form brown leaves and defoliation. Palms can die under heavy attack.

Ficus Whitefly is causing extensive damage on ficus hedges and trees in Dade County. Leaves yellow and hedges and trees become bare if not treated. Treat with Organocide at weekly intervals for 3 weeks to give control. Trees and hedges grow back if treated. Ficus benjamina is a favored host but this whitefly also attacks other ficus. Dade County has released natural predators to control the outbreak before it spreads.

Palm Weevil borers attack newly planted or stressed palms and causes the top of the palm to lean over and eventually to fall off. Date and sabal palms are favored hosts.

More New Insect Pests Added 1-09

A new soft scale is recent addition to the exotic pest population of South Florida. The croton is a preferred host plant but this scale can also attack guava, strangler fig, mysore fig, mango, firebush, wild coffee, marlberry, and satinwood. The female scales are greenish-yellow with dark striations. Male scales have a glassy appearance. This new pest does not have any natural enemies at present. Pesticides like Organocide, and Safer’s Insecticidal Soap should offer control on the open growing croton. Apply when the temperatures are below 85 degrees and when there is no wind. Reapply in 10 days to kill hatching eggs.

Added 8-11-2009

Laurel Wilt is a new disease threatening avocado trees in South Florida. This disease was first noted in North Florida where many native red bay trees were dying. The disease was just discovered in South Florida at the University of Florida’s Tropical Research and Education Center in Homestead in Miami-Dade County. The county has over 6500 acres in commercial avocado production and the crop is valued at 40 million dollars by commercial growers in the area.

Laurel Wilt poses a serious hazard for homeowners who are growing the tree for their own consumption. The disease is spread by the red ambrosia beetle which bores into the tree and spreads the disease through its mouthparts. The beetle attacks living trees, pruned and injured trees, stumps, and severed branches. Trees can die from 21 days to 3 months depending on tree condition. The disease is spread by movement of infested wood, wood chips from infested trees, illegal dumping of infested wood, using landfills that do not burn or bury infested wood, and moving plants of red bay and avocado that might be infested.

Trees will wilt, leaves will turn to dark green/brown and hang on the tree, Stems and trees will die back, and trees will have boring holes with whitish sap and the inner sapwood will have dark streaks. Sapwood normally is white without dark streaking. Call 1-888-397-1517 if you suspect activity on your avocado or red bay.