Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 11/3/2003
Publication Date: 11/3/2003
Citation: TROUT, T.J., SCHNEIDER, S.M., AJWA, H.A., GARTUNG, J.L. FUMIGATION AND FALLOWING EFFECTS ON REPLANT PROBLEMS IN CALIFORNIA PEACH.. INTERNATIONAL CONFERENCE ON METHYL BROMIDE ALTERNATIVES AND EMISSIONS REDUCTIONS. 2003. Interpretive Summary: When peach and several other types of fruit and nut trees are replanted after a previous orchard is removed, the trees often grow slowly. Growers have learned that fumigation with methyl bromide reduces this "replant disorder" and the new trees are more vigorous and grow more uniformly. The causes of replant disorder have not been identified but are believed to result from a complex of major and minor soil-borne plant pests whose populations evolved with the previous orchard. We are pursuing chemical and non-chemical strategies that reduce the replant problem in peach and plum. Fallowing up to 3 years improved tree growth and yields and reduced nematode populations. Drip-irrigation applied 1,3-D and chloropicrin combinations reduced nematodes below measureable levels to 5 ft depth for up to 3 years and gave yields comparable to methyl bromide fumigation. Drip-applied chloropicrin alone gave the best tree growth in one trial. Fallowing can reduce the replant problem, but is costly for farmers. Drip-applied fumigants can work as well as methyl bromide. The benefits of these treatments tend to decrease with time because, as long as a moderately healthy tree is established, through pruning and thinning, even less vigorous trees tend to catch up with the fumigated trees. About 20 to 40 kg of extra fruit per tree is required to pay the costs of fumigation.
Technical Abstract: Methyl bromide will no longer be available for soil fumigation after 2005. It is an important pest control material for replant of orchards that suffer from "replant disorder". Several field trials tested effects of fallowing and drip-irrigation applied alternative fumigants. In all cases, methyl bromide and 1,3-D products eliminated the plant parasitic nematodes for 1 to 3 years. Herbicide root kill and lime urea treatments did not reduce nematode counts. Increasing fallow periods, especially 2 and 3 year, dramatically reduced nematode counts. One year of fallow increased tree growth in all four studies. Each additional fallow year in one study resulted in improved growth and third year yield, and yield and growth after 3 yrs fallow was within 10% of that with MeBr fumigation (with no fallow). The drip-applied Telone and Telone C-35 products always gave significantly better growth and yields than the no-fallow checks and yield equal to those with MeBr fumigation. Drip-applied chloropicrin gave the highest growth and yield in the one test where it was used. . The benefits of these treatments tend to decrease with time because, as long as a moderately healthy tree is established, through pruning and thinning, even less vigorous trees tend to catch up with the fumigated trees. About 20 to 40 kg of extra fruit per tree is required to pay the costs of fumigation.