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Poster: Biology & Disease Mgmt: Chemical Control


Evaluation of soil conditioner OR079 for the optimization of metalaxyl in control of Phytophthora nicotianae in Texas citrus orchards
P. DUBERNEY (1), J. Hernandez (1), V. Ancona (1) (1) Texas A&M Kingsville Citrus Center, U.S.A.

The Texas citrus industry faces a great problem with the control of foot and root rot disease caused by Phytophthora nicotianae. P. nicotianae infects feeder roots and the trunk of trees causing poor water and nutrient uptake leading to yield loss, fruit size reduction and tree decline. Treatments for Phytophthora diseases are limited, therefore optimization of available products is of great importance. We hypothesized that the effectiveness of metalaxyl in reducing P. nicotianae soil propagules can be increased when applied in combination with the soil conditioner OR079. To test our hypothesis we applied metalaxyl, OR079, and metalaxyl plus OR079 to mature grapefruit trees with Phytophthora infection and quantified Phytophthora propagules in the soil. Phytophthora propagule counts were assessed at 4, 8, and 12 weeks post treatment and compared to an untreated control. Results showed that all treatments had significantly reduced Phytophthora counts in the soil at 4 and 8 weeks post application compared to that of the untreated control, but were not statistically different to the control by 12 weeks. Moreover, OR079 did not increase metalaxyl effectiveness in reducing Phytophthora propagules but reduced its activity when mixed. In addition, application of OR079 and metalaxyl significantly increased citrus fruit size. These results indicate that timely treatment for Phytophthora infection improves root health and water uptake leading to increase citrus fruit quality.