ISSUE 15 September 17, 2009
BROADLEAF CROP DISEASE RECAP: IMPLICATIONS FOR NEXT YEAR
Sclerotinia (white mold) has impacted dry edible beans, sunflowers, canola, soybeans, and pulse crops to some degree this season. The greatest severity I have observed has occurred recently in edible beans and in sunflowers. There is nothing that can be done about the disease this late in the season. When planning for next year, you may want to take a few pieces of information into consideration. High levels of white mold mean that lots of sclerotia will be produced and dropped to the soil; this will potentially lead to a very high inoculum load for next year. It is important to make sure that your rotations between susceptible crops are long enough, particularly in the fields that are currently full of sclerotinia. Although crop susceptibility varies, current recommendations suggest a susceptible crop should be planted only one in four years. However, even if recommended rotations are followed, it may be wise to budget in a fungicide application. If the environment is not suitable for disease, it might not need to be applied, but if the environment looks suitable for disease during bloom, it might be well worth it.
Rusts. Dry bean rust is being observed in a couple counties, but showed up very late. It is likely that the occurrences are the new race, virulent on most (if not all) varieties grown. We dodged a bullet this year, but the race is still with us. It will be important to keep an eye on it next year; just because it didnít cause a widespread epidemic this year does not mean it wonít be an issue in the next.
Sunflower rust showed up very early this year. However, the disease was local and progressed very little throughout much of June and July. It appears to have caught fire in August in some locations, in which much of the acreage was justifiably treated with a fungicide. The pathogen causing sunflower rust will overwinter again, but the time it will occur next year is unpredictable. Prior to 2008, it was very rare to see it before late July or August but in the last two years it was observed in June. Should it occur early again, a fungicide application will likely be necessary where it is found.
Soybean rust has blown up recently in the South, but is a no show further north. Hopefully this trend continues, just donít forget about it.
Bacterial Diseases. The occurrence of bacterial diseases on some crops appeared to be relatively high. Good rotation strategy and clean seed are the best preventative management strategies for bacteria. I encourage those afflicted by bacteria to do their best to prevent diseases. Remember, fungicide applications are generally not effective and/or practical for bacterial disease management.
Root Rots. Root rots are a distinct possibility in some crops, but less likely in others. However, when planning for 2010 consider a few things that tend to increase the likelihood of root rots. 1) History of a problem. If you have had stand establishment problems or known root rot damage in a field, you are more likely going to see it again the next time you go back to that crop. 2) Short rotations, when growers go back to a field with the same crop every other year (or more frequently) your likelihood of root rot pressure increases, 3) Water, lots of water will often provide a favorable situation for root rots, if you have poorly drained fields or heavy soils your likelihood of disease may increase.
Seed treatments are a relatively inexpensive way to help prevent the establishment of root rot pathogens immediately after planting. This window is a critical one; the seed is pretty susceptible as it sits in the cool soil. In most situations, select a broad spectrum product, with a fungicide that works on Fusarium and Rhizoctonia, and a fungicide that works on the Pythium and Phytophthora. Additionally, protect against seed-borne Ascochyta if you are growing a pulse crop.
Selecting a resistant variety can prove critical for root rot management, particularly for Phytophthora management in soybeans. The most recent race survey of the phytophthora pathogen indicated that the resistance genes RPS 1K and 6 were most likely to be effective against the majority of races in North Dakota. This may still be true, but there are very clear examples where the 1K gene is no longer effective in certain fields. This is probably a more frequent situation in Richland and Cass counties, but could exist elsewhere. Additionally, there may be fields where the 6 gene is ineffective, I just havenít observed it myself. If you know a soybean field had significant root rot pressure, and you know which gene you had in the variety, it is time to switch the gene. Rotation between genes is a good management practice that will slow race changes in your field anyhow.
Ascochyta. Ascochyta on pulse crops remains an important issue. I saw some very severe Ascochyta this year, but it was localized. When the environment is suitable, a fungicide application(s) will be necessary on chickpeas, likely beneficial on lentils, and probably beneficial on peas. It is a good practice to have that in the back of your mind when planning for 2010.
Pasmo on Flax. Recent fungicide trials have indicated that pasmo on flax is yield reducing, and that a single fungicide application can significantly reduce disease and increase yield. Trials initiated by Scott Halley in Langdon have been very promising, and this information will be available in the future. Something to consider, perhaps.
Extension Plant Pathologist