In the last update, I commented on how the dry weather pattern that we had experienced in the desert southwest has greatly reduced the progression of diseases such as downy mildew that thrive when relative humidity and free moisture are abundant. Well, as we know, the weather can change rapidly in the desert. Now, with the wet conditions experienced this past week, one should look for increased activity for diseases such as downy mildew and Sclerotinia drop, among others. However, do not forget that in the first half of January, crops were subjected to several nights of temperatures at or below freezing in many areas. The results of that physical damage may become more apparent as crops progress to maturity. Also, as mentioned in the last newsletter, crops that have sustained freeze damage should be monitored carefully in the weeks ahead for the appearance of disease symptoms caused by opportunistic microorganisms, which can colonize freeze-damaged tissue and cause additional deterioration of plants.

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To contact Mike Matheron go to: matheron@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.