2019-11_18-036C – Cover crops and nematicides: comprehensive nematode IPM across the grove landscape

Cover crops and nematicides: comprehensive nematode IPM across the grove landscape

Report Date: 02/05/2020
Project: 18-036C   Year: 2019
Category: Horticultural & Management
Author: Larry Duncan
Sponsor: Citrus Research and Development Foundation, Inc.

Fall 2019 nematicide treatments were initiated in September and continued throughout October. Effects on nematode populations were measured (as previously described) in December. Randomly assigned pairs of the new materials were rotated (one of each pair in spring, the other in autumn) to comply with annual rate limits and to reduce the occurrence of pesticide resistance in the sting nematode populations. Oxamyl and aldicarb were not rotated with other materials. Oxamyl was applied twice in each of spring and fall. Aldicarb was applied just once in April, per label requirements prior to deregistration. All nematicides except oxamyl (which was sprayed by hand during the final third of the irrigation cycle) were injected for two hours, beginning 30 minutes after irrigation began and ending a half hour before the irrigation run ended. This injection period was double that used in the spring applications and it appears to have produced more favorable results. One pair of new products reduced sting nematodes by 67%-84% (depending on the order of treatment) and the other pair by 19%-47%. Oxamyl reduced the nematodes by 62% and aldicarb had no effect on the sting nematode population. Growth of the trees as measured by trunk cross sectional area between February and December was greatest (P=0.05) for the oxamyl treatment. Growth of trunks in no other treatment was significantly different from the control; however there was an inverse linear relationship (P=0.02) between trunk growth and the average sting nematode population density (log-transformed) for each treatment measured in June and December 2019. Numbers of fruit on the young trees and dropped fruit were counted in November. Although fruit count was positively related to trunk diameter (r= 0.63, P=0.000), there was an pronounced inverse relationship between fruit number and trunk growth during the 2019 season (n=224, r= -0.63, P=0.000). Fruit count was unrelated to nematode population density.
In the perennial peanut trial the trunk girth in November was inversely related to the sting nematode population density measured the previous summer in the row middles. However, ANOVA detected no effect of cover crop on trunk girth. Although root mass density was four-fold in peanut compared to native vegetation in both July and December, the sting nematode population in peanut was just a third of that in native vegetation during 2019 (P=0.04). Unlike in the nematicide comparison trial above, oxamyl did not reduce the sting nematodes measured in December in the tree row. Possibly, the lower population density (by two thirds) in the peanut trial compared to the nematicide trial obscures effects of management on population density. Fruit count was related (r=0.93) to the trunk girth, but was not affected by cover crop or oxamyl.

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