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 MOFGA's 2011 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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MOFGA's Pest Report - June 30, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight Update And Other Tomato And Potato Spots: At this time late blight is not being reported in New England. BUT, there was a recent report in New York, on Long Island. At this time, it is restricted to a few farms. Remember, things can change quickly. It is time to be vigilant and be out scouting, especially if the weather becomes wet again.

Also, you should learn to recognize some other tomato problems. Be ready and able to distinguish the common blights and spots. Don’t jump to the conclusion that you have late blight. Here is a website with great pictures:


The three most common problems with tomatoes grown in the field in Maine are Early Blight (potatoes too), Bacterial (Spot and Speck) and Septoria Leaf Spot. It is early, but it is time to start looking if you want to get some control on them. Other issues that may sometime trick growers into thinking they have late blight are heat stress and Botrytis. See that website above for pictures of all of these.
  • Bacterial Speck starts as dark brown to black spots on leaves that later develop yellow halos around the area effected. On the fruit black specks develop that rarely get larger than 1 mm . Bacterial Spot starts as brownish, circular spots that may become as large as 3mm and irregular. The diseases may be seed borne and may be carried over in weeds. High humidity and low temperatures favor bacterial speck.
  • Early blight of tomato is caused by fungi and starts on the lower leaves as small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas as the spots enlarge. Later the tomato fruit may rot on the stem end. The disease is carried over on tomato residue in the soil and can be seed borne.
  • Septoria Leaf Spot is a fungal disease that starts as spots on the lower leaves that have a dark brown margin and a tan center, and no target appearance. Rapid defoliation can occur.
Crop rotation is the first line of defense from all of these problems. Sanitation is important, especially for late blight that only survives the winter on living tissue such as the potato tuber. Do not grow tomatoes or potatoes near cull piles of last year's crops. Trellising, staking, cages, etc help but remember to disinfect if they were used last year (a 10:1 dilution of household bleach is effective). Prune off diseased lower leaves, but it is especially important to disinfect tools if the problem is one of the bacterial diseases. Avoid working in the crops when they are wet. Scouting is going to be important this year. With wet weather, start early and if you decide to use a material, copper is probably the one most effective for us organic growers. Remember, you MUST use a formulation that is approved for organic production. The ones that I know are approved are Champ WG, NuCop 50 WP. Others may be but check with your certifier BEFORE using. You must use copper in a way that does not lead to contamination of the soil or crop. Follow the label instructions, and maintain a good crop rotation to avoid use of copper in the same field too frequently. Regularly do soil testing to monitor your copper levels.

Potato Leafhopper Update: Potato leafhoppers are here. Scout your potatoes, beans and strawberries. For details on description, life history, and management see the last issue of the Pest Report (June 23, 2011)

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