Management
Host resistance is the primary method of control for Phytophthora sojae. There are three types of resistance: R-gene mediated resistance, root resistance, and partial resistance. Currently there are 14 Rps genes, meaning 14 different single-resistance genes, which have been identified for R-gene mediated resistance and mapped in the soybean genome. Effectively, the most damage that the oomycete can induce is a lesion. Root resistance is inherited and is generally expressed in the roots. In this case, the stem of a germinating seedling is most susceptible. Once the first leaves begin to emerge, the partial resistance of the plant is expressed. Colonization is reduced and lesions are smaller in comparison. This management prevents the zoospores from germinating in the root tip and therefore unable to produce hyphae, which it needs to survive.
Phytophthora sojae can also be controlled using fungicides. For example Metalaxyl, a fungicide that is specifically used for oomycetes, is used for treating soybean seeds. It’s used to prevent seed decay and pre-emergence damping off. This fungicide has been observed to be more effective on highly-tolerant soybean plants. Metalaxyl is most effective when applied to the soil as it allows the plant to take it up through the roots and elongate the control period in comparison to a seed application. Metalaxyl prevents the spores of Phytophthora sojae from entering the soybean plant tissues. As with all fungicides, Metalaxyl is effective for prevention only and should be applied before the disease has established itself inside the tissues of the soybean plant. Replanting must be done once severe pre-emergence damping off is observed.
Improving field drainage and soil tillage are cultural practices that can help minimize the effect of Phytophthora sojae. Improving soil tillage can help eliminate oospores from the soil. Oospores are very sturdy and can remain stagnant in the soil for a long time and therefore crop rotation alone is not effective. Proper field drainage prevents flooding and therefore inhibit zoospore movement towards the host.
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