Thursday, April 24: The weather forecast is suggesting that we may have a 24-hr wetting period with mean temperatures slightly above 50 F from 7 PM on Friday through at least 6 PM on Saturday. The forecast is for scattered showers, so whether or not we get enough wetting to allow infection by fungal diseases remains to be seen. Nevertheless, it would be prudent to apply a fungicide tomorrow morning on any stone fruits that are in bloom so as to prevent development of brown rot blossom blight. At the Hudson Valley Lab, apricots and some cultivars of Japanese plums are now in bloom (see photo below).
Japanese plums are generally less susceptible to black knot than are common European plum cultivars such as ‘Stanley.’ Nevertheless, considering how devastating black knot can be if it is not controlled, plums that are at white bud or in bloom should be protected with chlorothalonil prior to the rains predicted for Friday night, especially if there is any history of black knot infection in the blocks in question. As always, read the product label before making any fungicide applications. Some, if not all, of the chlorothalonil labels specify the crops may not be retreated at intervals of less than 10 days.
‘Early Golden’ plum in bloom at the Hudson Valley Lab at noon on April 24.
Brown rot mummies (left) and black knot (right) in a plum tree. As noted in a previous post, both should be removed before rains begin tomorrow because they will supply inoculum for initiating disease during the coming season.
