Ask a Master Gardener: Skeletonizer moth larvae the cause for brown grape leaves

Q: My grape leaves are falling off after they turn papery brown. I've noticed small, yellowish-green worms with black bands around their body on the leaves. What are they and how can I prevent brown leaves?

A: The culprit is the grape leaf skeletonizer which I had trouble with this year. The blue-black-colored moth about a half-inch or so long emerges in spring (usually June) and lays clusters of light tan eggs on the underside of grape leaves. They hatch, turn brownish and then develop into yellow-green larvae, all the while eating the grape leaves. The leaf then becomes a brown "skeleton" with only the veins left.

They move quickly from leaf to leaf - you can lose all the leaves on your grapevines by August. This happened to me last year but did not affect the crop this year.

To control the skeletonizer, you can remove the larvae by hand, but be careful, they have stinging hairs and the hairs can become airborne and breathed in. A biological control spray is bacillus thuringiensis (BT), or for chemical control use carbaryl. I used one good application of a pyrethrins spray mixture about June 20 which took care of them for about three weeks, then I had to reapply. Be sure to follow directions and read the labels of any product you purchase and spray when under 90 degrees, early morning being best.

Q: The leaves on the bottom of my tomato plants have turned brown and I hardly have any tomatoes. What can I do to get them producing and keep the plants alive?

A: This is a common problem and we saw a few examples of this at the July 14 "Ask the Master Gardener" workshop. There are many different types of bacteria, fungi, viruses, insects and nutrient deficiencies that cause problems. Too much or too little watering can make leaves turn yellow. Do not water from above and wet the leaves as this will spread diseases. Water enough to flush the salts away from the roots. Since the temperatures have been above 90 degrees, our tomatoes are suffering and yellowing leaves are a result.

Fewer tomatoes could be the result of a pollinating issue. Nitrogen deficiencies can cause leaf yellowing also. Be sure to fertilize per package instructions. A magnesium deficiency could be the culprit - mix 2 tablespoons of Epsom salts per gallon of water, but also add sulfur or the magnesium will not be effective.

If you have brown or gray spots on your leaves and they then turn brown, it could be a fungus called Early Blight (A) or Septoria Leaf Spot. A fungicide can be applied if you suspect these. Remove the affected plant, including all the leaves remaining on the ground as the virus can stay on them over the winter. Do not plant tomatoes in the same area for the next 3 or so years.

Fusarium (F) and Verticillium (V) wilts are fungi that cause yellowing of older leaves - they turn downward and droop. Get plants that are resistant to these fungi - they have the codes V, F, N, A and T. (N) is for root-knot nematode. (T) is for mosaic virus.

You can sterilize the soil after your tomatoes quit producing by applying a quarter-mil thick clear plastic over the soil for at least a month. The soil will heat up, destroying bacteria, fungi and insects (it will also affect beneficial insects).

Finally, if you have any part of the plant that is alive by September, it is possible the lower stem will produce new growth and form tomatoes that can be harvested by the first frost later this year.

Q: My lawn does not look so good this year. How much water should I apply?

A: The windy, dry days this year, with no rain in May and June, were hard on lawns. There are many variables related to how much to water. It depends on the type of grass, rainfall, humidity and your watering system, among others. Generally, the roots of grass reach into the soil about 4 to 6 inches. Water needs to get to the bottom of the roots just like any other plant. It takes about one inch of water to reach ends of roots, depending on whether soil is sandy, loam or clay.

To measure this, place tuna cans (or any other low container about the same size) on various areas of your lawn. If your lawn is large, you may need 15-20 containers, if small, you may only need 4-6. Turn on your watering system and note the time it starts. When you think you have about a half-inch of water in the containers, turn it off and note the time. Measure the depth. If it's a half-inch of water, double the time. It is not good to water grass 10 or 15 minutes at a time unless you know about one inch is applied during that time. Shallow watering does not promote deep root growth and lawns dry out quicker.

Now you need to know how often to water based on type of grass, temperature, humidity and winds. Most of us have figured that out ourselves, but to learn more, be sure to watch for the Master Gardeners Workshop on "Irrigation" in August. Come by the University of Arizona Mohave County Cooperative Extension office at 101 E. Beale St. or call 753-3788 for more information.

(The University of Arizona Mohave County Cooperative Extension - http://extension.arizona.edu/publications)