Posts Tagged ‘tomato late blight’

Vegetable Disease Update – July 2, 2010

Friday, July 2nd, 2010

Bob Mulrooney, Extension Plant Pathologist;

Cucurbit Downy Mildew
We are at minimal risk at the present but keep up to date by checking the ipm PIPE website regularly for updates. Downy mildew was found in New York state for the first time on cucumber in Erie and Niagara counties close to the Ontario, Canada infection site. The northern march of downy has been slowed. We have had some weather patterns coming north but the clear skies and plenty of UV radiation have probably been keeping viable spore number low. We are checking our sentinel plots weekly for downy mildew here in DE.

Bacterial Wilt
Bacterial wilt on slicing cucumbers was diagnosed this week. Symptoms on this planting were random wilting of several runners on 20% of the plants. Sticky strands of bacterial ooze can be seen when the cut ends of the wilted runners are touched together then slowly drawn apart. Striped and spotted cucumber beetles carry the bacteria on their mouthparts and inoculate them when they feed on the succulent stems early in the season. Bacterial wilt is not seed borne and does not persist in the soil more than 2-3 months. It is thought that the bacteria acquire the bacteria from infected weed or volunteer cucurbit hosts. Cucumber beetle control is the primary control method.

Strands of bacterial ooze from touching cut ends of infected runner and pulling them apart slowly

Potato and Tomato Late Blight Webinar for Home Gardeners
Rutgers, Penn State and Cornell University vegetable plant pathologists will be holding a Webinar on Potato and Tomato Late Blight for home gardeners on July 13, 2010 at 6:30 PM. You are encouraged to participate in this timely topic. The linked announcement has all the information to enroll. It will be a good review for commercial producers as well.

Pythium Blight or Cottony Leak on Snap Beans
Pythium blight or cottony leak on snap beans was diagnosed early this week. This disease likes the hot, humid conditions that we had before this recent break in the weather. When we go back to the humid weather again with scattered showers and irrigation this disease can be a threat. Look for the cottony white growth in the lower canopy and on pods close to the ground. There is a 24c registration for Ridomil Gold Copper (2 lbs/A) for prevention of Pythium blight in DE, MD and VA. Several applications may be necessary if favorable weather persists.

Cucurbit Powdery Mildew
Powdery mildew on cucurbits has been reported in New Jersey. Delaware growers should be scouting and begin applying fungicides for powdery mildew once 1 old leaf in 45 has been found with powdery mildew. See the article titled Powdery Mildew on Cucurbits in WCU 18:15 for suggested fungicides.

Potato and Tomato Late Blight Update

Friday, June 25th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Late blight on tomatoes was found on Long Island in a home vegetable garden this past weekend. There have been no reports of late blight in DE, NJ or eastern shore VA to date. The high temperatures this week (above 90°F) are not favorable for late blight.

Late Blight Update

Friday, June 4th, 2010

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Unfortunately late blight has continued to appear in tomatoes over the past week. Locally, a second high tunnel outbreak in St. Mary’s County, MD was confirmed last week. This is the second confirmation in Maryland and is about one mile from the first outbreak. So far no other outbreaks in Maryland and none in Delaware have been reported. In other states, an outbreak in a Pennsylvania greenhouse was confirmed on May 17 (that crop was destroyed).

In northern Kentucky on May 27, infected transplants were found in one home garden and several box stores. These transplants had been grown outside of Kentucky and shipped to the box stores for sale. The stores involved are national chains. The transplants, which are destined for home gardens, pose a huge threat because they would provide widespread dispersal of inoculum. We hope to avoid a recurrence of this scenario, which caused widespread commercial losses in 2009. Everyone is encouraged to be vigilant. If late blight is suspected – please contact your extension educator.

Again I am recommending that commercial tomato growers apply a protectant fungicide such as chlorothalonil (Bravo), Gavel, or mancozeb. Scout aggressively for symptoms and switch to more targeted translaminar products when late blight is found.

Late Blight Reported on Tomatoes in Maryland and Pennsylvania

Thursday, May 20th, 2010

Bob Mulrooney, Extension Plant Pathologist;

There was a confirmed report of late blight on greenhouse grown tomato transplants and in a high tunnel in southern Maryland. This is an isolated occurrence and should be no threat to our area at the present time. This outbreak highlights the continued need for timely scouting of tomatoes and potatoes for the early symptoms and signs of late blight.

Just breaking news is that there was a late blight report from Pennsylvania. Beth Gugino, Extension Vegetable Plant Pathologist at Penn State reports that “at the end of the day on Monday, late blight was confirmed (sporangia observed) on locally grown greenhouse tomato transplants in the Northwest region of Pennsylvania. The grower has destroyed the symptomatic plants and is adjusting his fungicide program. The PA Department of Ag is currently conducting a site visit and is working with the grower to avoid potential spread.”As I said before keep a close watch on emerging potatoes and tomato transplants.

Late Blight in Southern Maryland

Thursday, May 20th, 2010

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Late blight on tomato occurred early in 2009 throughout the East Coast. Because the disease arrived early and was disseminated widely on infected transplants, growers had to apply fungicides season-long to maintain crop health. Unfortunately on May 7, 2010 a greenhouse outbreak of late blight on tomato was found in St. Mary’s County, MD. The grower destroyed the tomatoes in his greenhouse, but kept some high tunnel production, where the disease is being managed with fungicide applications. We do not know how late blight became established or whether it will spread quickly. The surrounding fields have been scouted extensively and no additional infection has been found. The disease is favored by cool wet weather, which often occurs in spring. Therefore, tomato growers should scout their crop rigorously and apply fungicides as described below.

Late blight is caused by the fungus-like organism Phytophthora infestans, which is an obligate parasite. The organism prefers cool moist weather and cannot overwinter in Delaware or Maryland (outside a living host) because only one mating type is known to occur in these states. (If the other mating type is introduced, the pathogen would be able to form resistant oospores.) In the absence of resistant oospores, the late blight fungus overwinters in infected potato tubers or is introduced into an area on wind, or infected plants. We don’t believe that the pathogen overwintered in St. Mary’s County, however we don’t know how it was introduced. The grower did not have any live plants that could have allowed late blight to overwinter.

Phytophthora infestans can infect leaves, stems and fruit of tomatoes (Figures 1-3). Lesions on leaves are large and dark brown. Purplish or whitish growth on the lower surface of the lesions occurs under humid conditions. Fruit lesions initially appear water soaked, turn dark brown, expand rapidly, and are shiny.

There are several fungicides available that will help reduce disease spread. No fungicide however, will eradicate the disease. To be most effective, fungicides should be applied prior to disease onset. For this reason, once plants reach a height of 6 inches, protectant fungicide should be applied every seven days. Chlorothalonil (Bravo), Gavel or mancozeb are good choices.

Once the disease is observed in the area, switch to a translaminar fungicide which can move into and through the leaves. Also, it is important to note that while the most common previously occurring P. infestans genotypes were resistant to Ridomil, the genotype that occurred on tomatoes in 2009 (called US22) is sensitive to Ridomil. In addition, there are several other fungicides listed in the Delaware Commercial Vegetable Production Recommendations, which can be used for late blight management.

Rotate between the following tank mixtures:

● Curzate–3.2-5.0 oz 60DF/A plus a protectant fungicide
● Forum–6.0 fl oz 4.18SC/A plus a protectant fungicide
● Presidio–3.0–4.0 floz 4SC/A plus a protectant fungicide
● Previcur Flex–1.5 pt 6F/A plus a protectant fungicide
● Ranman–2.1-2.75 fl oz 400SC/A plus a protectant fungicide
● Revus Top–5.5–7.0 floz 4.16SC/A plus a protectant fungicide
● Tanos–8.0 oz 50WG/A plus a protectant fungicide
● Reason –5.5 – 8.2 fl. oz plus a protectant fungicide



Late blight symptoms on leaves (Figure 1), stems (Figure 2) and fruit (Figure 3) of tomato (images courtesy of Dr. Meg McGrath, Cornell University).

Information on Potato and Tomato Late Blight Management

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist;

With the widespread occurrence of late blight last season on tomato and potato. There is some new information available from other universities that might be of interest. Dr. Meg McGrath, Cornell plant pathologist on Long Island, has written two articles on managing late blight organically, both of which are available online: Managing Late Blight in Organically-Produced Potato and Managing Late Blight in Organically-Produced Tomato.

Dr. Tom Zitter, also from Cornell, compiled a list of tomato varieties with reported resistance to late blight and early blight that might be helpful: Table of Late Blight and Early Blight Resistant Tomato Cultivars