ISSUE 2 May 11, 2006
SEEDBORNE DISEASES OF PULSE CROPS
Due to regional disease problems in some pulse crops (dry pea, lentil and chickpea) last year, it may be a good idea to have seed tested for the presence of Ascochyta diseases before planting. Seed can be tested locally at the North Dakota State Seed Department and North Dakota State University plant diagnostic lab.
Although all three crops are affected by Ascochyta diseases, different fungal pathogens cause the disease on each crop.
On lentil, Ascochyta blight is caused by a fungal pathogen specific to lentil. Ascochyta blight can be transmitted readily from the seed to the seedling at a fairly high rate. For this reason, growers should have their lentil seed treated with either LSP or Mertect if Ascochyta is found in the seed. A recently obtained section 18 emergency exemption allows for the treatment of lentil seed with LSP or Mertect. Seed lots that have Ascochyta infections of more than 2 percent to 3 percent probably should not be used for seed.
On chickpea, Ascochyta blight is caused by a fungal pathogen specific to chickpea. Similar to Ascochyta on lentil, chickpea Ascochyta blight can be transmitted readily from the seed to the seedling at a fairly high rate. Because Ascochyta blight can be extremely damaging to chickpea, it is encouraged that seed lots with 0 percent infection be used. However, if disease-free lots are not available, then lots with less than 0.3 percent infection could be used if they are treated with LSP or Mertect. LSP and Mertect are available for use on chickpea seed through a special local needs section 24(c) label for North Dakota.
On dry pea, Ascochyta diseases can be caused by a complex of three different fungal pathogens that are specific to dry peas. Because the rate of disease transmission from dry pea seed to the seedling is so low, seed lots with up to 4 percent to 5 percent infection should be OK to plant. No fungicide seed treatments are currently available for dry pea that protect against seed-borne Ascochyta diseases in North Dakota.
Extension Plant Pathologist
NDSU POTATO BLIGHTLINE TO OPERATE IN 2006
The Plant Pathology Department at North Dakota State University will again be providing the potato blightline service at no charge to the potato industry of North Dakota and western Minnesota in 2006. This will be the twelfth year that this service has been provided and sponsored by Syngenta Crop Protection and Amistar fungicide. The hotline uses local weather data collected from weather stations throughout our area to forecast the occurrence and spread of late blight in fourteen non-irrigated and nine irrigated production areas in ND and western MN. The data is processed by the North Dakota Agricultural Weather Network (NDAWN) and analyzed by a computer program (WISDOM) to forecast when conditions are favorable for late blight to occur.
The forecast information is used by plant pathologists Gary Secor and Neil Gudmestad to make late blight management and fungicide recommendations. The recommendations are made Monday, Wednesday and Friday of each week during the growing season. The first late blight hotline will be Wednesday June 1st, and the hotline will continue through mid September depending on disease pressure. The hotline will also be used to confirm late blight infection and serve as clearing house for national late blight information. In addition to late blight forecasting, the hotline also provides cumulative P-values for early blight disease forecasting and management recommendations. Finally, it serves to alert growers of other disease and insect news, as well as posting messages of general interest such as potato field day dates.
The hotline recommendations can be accessed by phone or website.
The toll free phone number is 888.482.7286
The NDAWN website for potato disease forecasting, produced by Dr. John Enz of the Soil Science Department at NDSU, uses colored maps of ND to pictorially illustrate the late blight severity values (both two day and seasonal), favorable day values and P-day values for early blight throughout ND. That site is:
Go to applications and then the drop down box to potatoes.
Growers and scouts are encouraged to send suspect late blight samples to us for positive identification. It is important to receive samples as quickly as possible after collection. Leaf samples should be placed in a slightly inflated zip-lock plastic bag without a wet towel and sent to:
Gary Secor, Plant Pathology, Walster Hall 306, North Dakota State University, Fargo, ND 58105. Our phone number is 701.231.8362 and email address is email@example.com. We look forward to a successful potato year.
WHEAT STREAK MOSAIC VIRUS SYMPTOMS REPORTED
Wheat streak mosaic virus (WSMV) symptoms have been reported from two ends of the state, Sargent Co. and Bottineau Co. Symptoms in Sargent Co. were observed in planted winter wheat, while in Bottineau Co. they were observed in volunteer winter wheat. Symptoms of WSMV are the intermittent streaks and mosaic on the leaves (see close-up figure), and if severe, stunting of the plants. Fields with symptoms may show a range of yellowing and streaking symptoms (see field figure).
WSMV is controlled with cultural practices that break the cycle of the vector, the wheat curl mite. The volunteer wheat in Bottineau Co. has been destroyed with a burn-down herbicide prior to planting spring wheat in the area. For the winter wheat crop, the severity of the disease will depend on environmental stresses (disease and mite populations are more severe under heat and drought stress), the extent of infection, and the susceptibility of the cultivar.
WHEAT GROWING DEGREE DAYS
The North Dakota Agricultural Weather Network (NDAWN) is an excellent resource for information on weather and growing degree days (GDD) for a number of crops. The tools provided by this web site can help with fertilizer and pesticide decisions.
For wheat, the GDD information can be used for determining date of emergence and current growth stage. Current leaf stage provides information, for example, on when herbicides are needed and when the crop is too advanced for certain herbicides. If frost or wind damage causes loss of leaves, the GDD information provided by NDAWN would allow correct leaf staging in absence of some leaves. Correct growth staging also is important for fungicide decisions.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB UPDATE
Seed health testing is nearly completed. The lab is beginning to transition to the summer samples – what we call ‘general diagnoses,’ to differentiate from seed health testing and special testing that we offer. Some of the recent samples evaluated include a cucumber sample, transplanted into permanent beds under a high-tunnel greenhouse, which showed symptoms of environmental stress (no pathogen was detected). Although the root system was poorly developed, it did not show symptoms of root rot. The sample appeared to be suffering from severe transplant shock. According to NDSU Extension Horticulturist, Dr. Ron Smith, cucumbers grow better if they are direct-seeded in the planting site rather than transplanted. Another sample, a plum tree (digital images only), was examined by NDSU Research Specialist (tree pathology), Dr. James Walla. It appeared to have perennial canker, based on visual symptoms and what appeared to be fruiting bodies of the causal agent, Valsa cincta or V. leucostoma. This diagnosis could not be confirmed by the lab, however, since an on-site examination of the tree would be required to improve the level of certainty and accuracy of the diagnosis.
Digital images for diagnosing plant problems
Unfortunately, plant diagnostic lab personnel cannot make on-site inspections of samples. This is truly a limitation in certain circumstances, since seeing the ‘whole picture’ can greatly help improve the accuracy of a diagnosis. A possible solution to this problem is to include digital images or traditional photos with a sample. These images help provide clues and missing information to aid in diagnosing a problem, not only for tree and lawn samples, but also for crop samples.
Digital images are fantastic tools for diagnoses as well as physical samples. It is worth mentioning that disease diagnoses made from photos alone are less accurate – a physical sample is still needed if a disease is suspected. For insect and weed identification, however, good quality digital images alone (without a physical sample) can often lead to successful identification, as long as the identifying features of the insect or weed pest are clearly photographed (a camera with a macro lens for close-ups is invaluable!).
For all types of samples, physical samples alone sometime don’t tell the whole story, so including photos with a physical sample almost always improves the accuracy and level of certainty of a diagnosis. Several photos are ideal, with at least one showing the ‘context’ of the sample (the specimen of interest, along with the site immediately surrounding it) and several more images getting progressively closer to the problem. Images that get as close as possible while still being in focus are extremely helpful, along with images that show the big picture. Individuals are encouraged to bring or send images along with physical samples to their county agent. Or, images and samples can be sent directly to the NDSU Plant Diagnostic Lab, where a modest fee ($15-25) usually applies. Images can alternatively be emailed by the general public to firstname.lastname@example.org or to the local county extension office (the first eight letters of the county name @ndsuext.nodak.edu). If you are a county agent and a PDIS Submitter, you can easily check in sample information and submit images to the NDSU Plant Diagnostic Lab by using PDIS. Please feel free to call or email with questions.
NDSU Plant Diagnostic Lab
206 Waldron Hall, PO Box 5012
Fargo, North Dakota 58105