Pecans, peaches, plums and small fruit are susceptible to a large number of foliage, fruit, and soilborne pathogens. Field trials are conducted to evaluate candidate pesticides, timing of pesticide applications and to improve spray coverage to achieve safe, effective control procedures. Data from these trials are used to develop control strategies. I evaluate potential root knot nematode resistance in peach rootstocks for Texas fruit orchards. Brown rot of peach and plum, peach scab, root knot nematode control on peaches using fumigation, bacterial leaf spot of peach, black rot of grapes, pecan scab, downy spot of pecans, stem end blight of pecan, and root knot nematodes on pecans are diseases of fruit and nuts for which control strategies have been developed as a result of applied research conducted in Texas.
Shade trees are being killed in large numbers by one or more disease- causing pathogens. The most important disease of oak trees is oak wilt. I have been involved with other scientists to develop a control for this vascular wilt pathogen. Working as a team, field trials have been conducted on trees to evaluate the use of chemicals to control this fungus. In addition, I have conducted field trials to develop control programs for oak leaf blister, ball moss infestations and the parasitic plant, mistletoe.
Vegetables are susceptible to several foliage, fruit, and root pathogens. One of the goals of my program is to identify vegetable varieties that are resistant to one or more major pathogens. A second goal is to identify fungicide programs that can be used in conjunction with resistant varieties to insure maximum production of high quality vegetables. The principle diseases that have been studied are downy mildew of cucurbits, black rot of crucifers, virus diseases of cucurbits, bacterial leaf spot of peppers, white rust and downy mildew of mustard, and virus diseases of mustard and turnips.
As extension program leader, I have the overall responsibility for the extension plant pathology program.
Johnson, J.D., R.S. Halliwell, and J. Trampota. 1992. Effect of pecan scab
infection on nut quality (abst.). Phytopathology 84:498.
Halliwell, R.S., and J.D. Johnson. 1992. Incidence of lettuce infectious yellow
virus on watermelons in Texas. Plant Disease 76:643.
Johnson, J.D., and C.W. Horne. 1986. Strategies of controlling oak wilt in
Texas. Texas Agricultural Extension Service D-1286.
Appel, D.N., C.F. Drees, and J.D. Johnson. 1985. An extended range for oak wilt and Ceratocystis fagacerarum comparability types in the United States. Can. J. Bot. 63:1325-1328.
Revised December 2, 1996