Pecan Insect Problem

I have received numerous phone calls and samples this week from homeowners who have pecan trees with galls on the leaves and stems. Beginning in late April, galls or knots begin to appear on the leaf veins, leaf rachises, stems, catkins and nuts of the pecan. The galls, or knots, are caused by a minute, “aphid-like” insect known as the pecan phylloxera, Phylloxera devastatrix Pergande.

Infestations of pecan phylloxera have been reported to cause reductions in nut quality and quantity, premature defoliation and terminal dieback. When infestations are severe, it is not uncommon to find as many as 100 galls on a terminal. The galls of pecan phylloxera also serve as an alternate host for developing larvae of the hickory shuckworm.

Pecan phylloxera are found primarily in Texas, Louisiana, Mississippi, Oklahoma and Arkansas. Generally this insect is not found outside of the native range of pecan. Pecan phylloxera can be found on hickory trees and native pecan trees. It is particularly a problem in orchards containing large numbers of improved cultivars susceptible to it. Pecan phylloxera has been reported throughout Louisiana. Cultivars in Louisiana known to be susceptible to this insect include Stuart, Success, Schley, Caspiana, Desirable and Cape Fear.

In Louisiana, pecan phylloxera are active from late March through early June. Three generations occur annually. Only the first generation causes damage. Pecan phylloxera overwinter in the egg stage. The overwintering eggs are found primarily under the rough bark of the larger limbs, but they can also be found within old galls or any areas of the tree offering protection. The eggs hatch at budbreak.

The emerging nymphs, or “stem mothers” move from the protected areas to the opening buds and begin feeding. During this feeding process, a gall begins to form around the individual insect, eventually enclosing it. Eggs are laid by the “stem mother” within the gall. Toward the latter part of May, the galls split open, releasing large numbers of winged adults, or “winged-migrants.” These “winged-migrants” are yellow with smokey-black wings, and they are responsible for the dispersal of the insect throughout the orchard. They deposit eggs on the undersides of the leaves. When large numbers of eggs are deposited, the leaves take on a yellowish tinge. The eggs hatch into wingless males and females. After mating, an egg forms within the body of the female who, before dying, seeks out a protected area on the tree to overwinter.

Insecticides are the most common and effective way to control infestations of pecan phylloxera. When insecticides are used, they must be applied before galls form. Once the insect becomes deeply imbedded in the plant tissue and the gall begins to form around it, control is impossible.

Before any insecticides are applied, the presence or absence of pecan phylloxera should be determined. Pecan phylloxera can be easily observed with a hand lens or magnifying glass. Beginning at budbreak monitor trees regularly through April. If phylloxera are not present, no insecticide is necessary. If phylloxera are present, select and apply insecticide carefully. In some instances infestations may be orchard-wide, but infestations are more commonly limited to susceptible cultivars or portions of an orchard containing susceptible cultivars. Only trees known to the infested should be treated. Normally, only one application of an insecticide is required.

Galls formed by pecan phylloxera insect on pecan stems. Photo by Bobby Fletcher, Jr.

Citrus Scab Disease

I have also received several calls and samples of Satsuma fruit and leaves with a warty growth on them. This is a fungal disease caused citrus scab. Citrus scab is primarily a disease of Satsuma, grapefruit and lemons in our area. It does not affect oranges. Scab affects the fruit, leaves and young shoots causing irregular raised scabby wart-like outgrowths. Severely scabbed leaves and fruit become misshapen and distorted. The rind of scabbed fruit is thick and puffy.

Scab infections occurs on young growth in the spring and can be prevented by using Copper fungicides, tribasic copper sulfate or Kocide sprayed after bloom when the fruit is pea sized. Once the infection occurs, no control can be obtained. You need to get a copy of the Louisiana Home Citrus production guide at any Extension office or by going to www.lsuagcenter.com.

Citrus Scab symptoms on Owari Satsuma fruit and leaves. Photo by Bobby Fletcher, Jr.

Vegetable Update

The ripening of tomatoes in the garden usually brings in some devastating insects who seem to have a ravish desire for the tasty tomato fruit. I am referring to the green stinkbugs that pierce the fruit and destroy the quality and taste of the hard worked for tomato.

You have several insecticides to control these peaky insects. The first is carbaryl or Sevin, the second is Malathion and the third is Thiodan. Always read and follow label directions and make sure you adjust your water pH to 6.0 prior to mixing in the recommended amount of insecticide.

Remember that the Tomato Field Day is Wednesday, June 11th beginning at 5:00 pm with registration at 4:00 pm at Waterproof Ridge Farm located at 3719 Bayou Black Drive in Houma. Make sure you have your largest tomato entries ready as well as categories for the smallest tomato, ugliest tomato, best dressed tomato (school aged children only), and the most perfect tomato.

Bring in your vine ripened tomato and enter it in one of the categories such as largest vine ripened tomato at the LSU AgCenter “Tomato Field Day” on Wednesday, June 11, 2008 at Waterproof Ridge Farm in Houma. Registration begins at 4:00 pm and the program states at 5:00 pm.

For more information on these and other horticultural topics, call me at 985-446-1316, email me at bhfletcher@agctr.lsu.edu or stop by any Extension Service office.