Friday, May 4, 2012
Why are my Vegetable plants going blotchy?
Last week we had a full selection of Brassica Vegetables on the list Friday afternoon. By Monday morning we had to cancel all the orders. Grrrrrrr! Downy Mildew! I think it is more of a problem in small seedlings than plants growing in the garden but once the underside of the leaves is covered in grey fuzz we can't dispatch them.
Downy Mildew captured gardeners' attention a few years back when a new strain suddenly affected Impatiens, a species previously not bothered by Mildew. It has been a significant pest for seedling growers for many years, particularly in Brassicas and related plants such as Stocks and Alyssum. It's the Brassica vegies that send me over the edge, we have just moved into weather conditions that minimise the impact of White Butterflys and Diamond Backed Moths but the cooler, wetter weather introduces and new issue!
Anyway there is plenty of information on line about Downey Mildew in Vines that can be extrapolated to vegies, and some excellent research was done by Elizabeth Minchinton in the mid 1909's and the report is available via the NGIA web site.
The basics really, except for the surprise at the end: Good hygene, balanced fertilizer program (too much nitrogen makes the plants soft and succeptible to disease), ventilation (space trays and if possible punnets out) and plenty of light. Here's the surprise: Don't water in the morning! Peter says don't water in the aftrenoon, so the window around the middle of the day is pretty narrow. Why not water in the morning? The fungus spores are released through the moring and are avialable for infection at this time. It is also essential that the foliage is allowed to dry as quickly as possible because water on the leaves triggers spore germination. Only problem is controlling rainfall!
By the way if you do check the NGIA report the fungicide recommended Foli-R-Fos is available in home garden packs as Yates Anti Rot. Safe for people and pets, the product is actually Phosphorus acid.