Thursday, July 28, 2011

Tomato Leaf Mold

Ajay Nair
Department of Horticulture, Iowa State University

Tomato leaf mold is a fungal disease caused by Fulvia fulva. It occurs mostly under greenhouse conditions where relative humidity is high. When humidity is high, the fungus develops rapidly on lower leaves and
progresses upward. Significant yield reduction could occur if the fungus is not controlled early. Pictures shown below were taken in a greenhouse located near Cedar Rapids, IA in the second week of July 2011.

Symptom on upper side of leaves appear as small, pale green, or yellowish spots. On the corresponding lower side, the fungus sporulates producing darker colored area. Growers should consider taking following steps to manage tomato leaf mold disease:

1. Provide good ventilation in the greenhouse. Use fans to circulate the air inside
2. Whenever possible, keep relative humidity below 85%
3. While transplanting maintain adequate row and plant spacing to ensure sufficient air movement. Remove suckers to reduce shading and maintain proper plant growth
4. Avoid wetting leaves while watering
5. Reduce primary inoculum by disposing affected plant debris after harvest.
6. Some fungicides to control leaf mold include Dithane, Revus Top, Tanos, and Inspire. Use fungicides as per  label instruction and guidelines

Tuesday, July 26, 2011

Spray but not sway - Roundup damage on tomatoes

Ajay Nair
Department of Horticulture, Iowa State University

We are obsessed with things that are round.....cookies, pizza, pies, and now ROUNDUP !  Weed control had never been easy until the formulation called Glyphosate which is a non-selective, broad-spectrum, systemic herbicide and an active ingredient in Roundup. Care should be taken to minimize spray drift while applying this herbicide. Roundup spray drift can cause serious injury to non-target plants.

Pictures below show roundup damage on tomato plants growing inside high tunnels (compare with the rows behind). The entire row of plants growing on the outer edge of the tunnel was damaged due to roundup drift from adjacent field. Symptoms include distorted new growth with cupped leaflets. Extent of damage on tomato crop depends on factors such as  stage of growth, amount of exposure, cultivar, etc.
Precautions to avoid such damage:
1. Avoid spraying under breezy conditions
2. Utilize a shield to prevent drift over to non-target plants. 
3. When applying roundup near or in vegetable gardens, increase droplet size to minimize mist and possible drift.