Septoria leaf spot ( Septoria lycopersici) If the lesion has a yellow border and is occurring on the bottom of the plant, it is likely due to infection of either early blight or Septoria leaf spot. Firm, brown spots develop on tomato fruit. These stem lesions are a fairly distinctive sign of late blight and should definitely raise a red flag. Brown to blackish lesions develop on upper stems and leaf petioles. Leaf lesions begin as tiny, irregularly shaped brown spots and quickly grow larger – spots that are consistently small are most likely septoria leaf spot (see below). Sometimes the lesion border is slightly yellow or has a water-soaked appearance (see image). See Recognizing Tomato Blights for images.Ĭlassic symptoms are large (at least nickel-sized) olive-green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain). The most common symptoms on tomatoes are sunken, dark green or brown lesions on leaves and brown lesions on stems, with white fungal growth developing under moist conditions. We’re also trying to assess the presence of the pathogen by scouting fields, analyzing samples that come into the disease lab, and trying to catch the leading edge of the disease development here in Massachusetts.
Yellow blight definition update#
We’re tracking the weather conditions as well as we’re able – see the update on disease forecasting in this issue of Vegetable Notes. Assessing the risk for this season depends on those two things – favorable weather conditions and the presence of the pathogen. Spores survive up to one hour in sunny, dry conditions, and up to 4 hrs in cloudy weather. Favorable conditions for sporulation and areal dispersal are leaf wetness for more than 10 to 12 hours at moderate temperatures 60°-70☏. The 2009 growing season combined highly favorable weather for the disease (cool and moist) with numerous points of inoculation. This explosive growth is what devastated tomato and potato crops in 2009. The danger with this disease is that, under the right weather conditions, the development and spread of the pathogen can be explosive. Late Blight (Phytophthora infestans)Įffective management of this disease is largely dependent on an accurate assessment of risk, and knowing where and when the disease is present is a key component in assessing the risk to your crops. While it’s impossible to determine which pathogen is causing leaf symptoms without a lab confirmation, the information in this article may help you to distinguish a possible late blight infection from some of the other common blights. In any year, early detection and management of late blight is a key factor in minimizing the risk of an epidemic. The 2009 growing season was an excellent example of how bad the disease can be.
Given the right weather conditions and an early initial infection, late blight can be a devestating disease on tomato and potato crops.
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