Crop & Pest Report - All
Weather Forecast: July 30 – August 5
Climatological averages in the Northern Plains where highly variable weather is the true normal, tend to have little meaning when dealing with short term weather forecasting and clearly do not represent what should be expected on any given day. Yet, this next week, at least temperature wise, both minimums and maximums are projected to be near those 30 year averages. This will mean a lot of days with daily maximums in the low to middle 80s with morning minimums in the upper 50s to the lower 60s. There will of course be the normal day to day subtle variations but overall, the frequent weather swings so common in recent weeks appear to be taking at least a brief break.
The mean upper-level wind flow that had been from the southwest for much of the last week, that not only brought periodic thunderstorm events, but also many days with high dew points, has now transitioned to a more northwesterly flow. This will mean the next week will tend to be drier both in the sense of rainfall and also in low level atmospheric moisture content. Thunderstorms look spotty and light until perhaps the middle of next week (Figure 1) and dew point temperatures will be frequently below 60°.
With dew points generally low, relative humidity (RH) levels in turn will also trend lower for most of the next 7 days. Therefore, RH values will above 85% for fewer hours this week and mostly only during the traditional period in the early morning. Plus, during the other periods of the day the RH of the air will often be below 50% creating minimal disease stress on susceptible crops during this forecast period.
The projected Growing Degree Days (GDDs), base 34°, 44° and 50° for the period July 30 through August 5, 2015 are presented in Figure 2 and the number of hours where the relative humidity is expected to be at or above 85% can be found in Figure 3.
Assistant State Climatologist/Meteorologist
(701-231-8209) Twitter: @darylritchison
Most crops in the area are still looking great. After heavy winds on July 27th and 28th lodging could be a concern in areas. Winter wheat and some barley are beginning to be harvested. Sunflowers are close to blooming, scouting for disease and insect problems should continue to catch problems as they arise. Corn is beginning to look thirsty with leaves beginning to roll. Most hay in the area has been baled.
When considering replacing an alfalfa stand remember about autotoxicity. Alfalfa produces a chemical that can reduce the establishment and growth of new alfalfa into an existing stand or alfalfa residue. This effect can last in the soil for a variable amount of time after the stand has been destroyed depending on factors such as soil texture and weather. It may be best to plant an annual forage and wait a year to return to alfalfa if considering replacing a stand.
Area Extension Specialist/Cropping Systems
The region’s NDAWN stations indicate rain received during July 1-28 ranged from 0.6 inch (Tappen) to 4.4 inches (Carrington); and during April 1 to July 28 rainfall ranged from 6.9 inches (Robinson) to 15.0 inches (Jamestown). The region generally has adequate soil moisture to support row crop growth during the next month. Sunshine and dry weather would be welcome during August for favorable small grain harvest conditions and to reduce risk of disease development in row crops.
Winter cereal and barley harvest has begun with spring wheat harvest to soon follow. Harvest challenges include variability in plant stages, lodged plants, green weeds and moisture-saturated soils. Corn growth stages range from tasseling to blister, but majority of fields are silking (R1 stage). Based on NDAWN, accumulated corn growing degree day units from May 1 through July 28 continue to be similar to the long-term average for the period. Soybeans are in the pod development stages (R3-4). Mid-May planted dry bean are in the early seed development stages (R5-6). Haying continues to be a challenge due to wet conditions, contributing to reduced yield and quality.
The Carrington Research Extension Center’s annual Row Crop tour is scheduled for Thursday, September 3. The event will allow farmers and crop advisers to view corn, soybean and dry bean production research trials and receive current production recommendations. Event details will be publicized when program is developed.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center
We are nearing small grain harvest. Pre-harvest desiccant application is just starting on early seeded acres. The past week’s hot, humid weather has been great for row crop development. Corn is silking and the soybeans are up to R3 development. We are finding downy mildew on soybeans at the LREC. Downy mildew first appears as yellow flecks scattered on the top of the leaf (see photo). Eventually, the lesions will become brown with yellow near the edges. On the leaf underside, the fungal growth is a tan to grey look (to my eyes, it looks lavender). This disease rarely causes economic damage. For more information please see the soybean downy mildew article in the plant pathology section of this crop and pest report.
As the canola crop loses its flowers, look for blackleg early senescing. How is genetic resistance combatting the disease in your fields? Factors that contribute to blackleg are temperatures in the 70s °F and extended periods of canopy wetness. The maximum ascospore discharge occurs the second year following crop growth. So if you are using a two-year rotation, there is more inoculum awaiting suitable environmental conditions than wider rotations.
Area Extension Specialist/Agronomy
Beginning in late winter and early spring I was contacted by many folks in the region about media adds of adjuvants that contain nano-materials. Marketing information show claims that this technology will enhance herbicides and even control herbicide resistant weeds. My colleagues and I that conduct adjuvant research have not tested these products nor did we discover their availability any sooner than their marketing blitz. Below is an article about two nano-adjuvants written by Dr. Bill Johnson, Dr. Bryan Young, and Travis Legleiter, Purdue University July 20, 2015.
Adjuvants are very useful products which are used to enhance the activity of postemergence herbicides. Numerous adjuvant products from very reliable distributors are marketed annually and provide a true value to growers seeking to optimize herbicide performance. However, since the adjuvant industry is not regulated as stringently as the pesticide industry, we occasionally run into products that create a lot of attention because of extravagant claims made by the manufacturer or distributor.
Nanotechnology is a new and exciting area of research and product development in numerous sectors. Agrochemicals, including adjuvants, are being developed with nanotechnology and may very well have substantial benefits. However, during our winter grower meeting season, we began to hear rumblings about certain “nano” adjuvants and how they provided the answers for control of herbicide-resistant weeds. Our concern grew after reviewing the marketing material that inaccurately describes the underlying mechanisms of herbicide resistance and the suggestion that the only necessary action to control glyphosate-resistant weeds was to apply glyphosate with the nano adjuvant. The nano adjuvants purportedly would overcome resistance mechanisms and by promoting higher levels of herbicide penetration into the plant. No scientific evidence exists that would suggest weed resistance to glyphosate is simply a lack of foliar absorption. Nonetheless, we were getting phone calls about their utility and were hearing claims that there was university data to support their claims. However, we at Purdue University had not worked with these compounds, nor were we aware of university data supporting their use.
On the next two pages are copies of the “technical” data information provided by the distributors for two nano adjuvants. The information can also be accessed at the following web sites:
A number of interesting claims are made on these documents. In an effort to learn more about the utility of these adjuvants, we conducted a study at a site in Indiana with glyphosate-resistant Palmer amaranth and wanted to share the results in this article. Dr. Young has also collaborated with a number of other weed scientists throughout the Midwest to conduct similar trials and we will share the results as they come available.
Our trial was on glyphosate-resistant Palmer amaranth with a population of about 95% resistant: 5% susceptible. Control with glyphosate alone was 13.8%. There was a 5% increase in activity with one of these adjuvants at 27 DAT compared to glyphosate alone, but that only raised the level of control to 18% which is still well below commercially acceptable levels. In other words, the nano adjuvants tested did not solve weed resistance to glyphosate.
Adjuvants are critical components of making effective herbicide applications to control our most problematic weeds. However, the simple addition of an adjuvant to resolve weed resistance to herbicides does not exist. Be critical of any marketing claims that sound too good to be true, because most of the time they are.
Extension Weed Specialist
DEET as an Herbicide
Question: I have an interesting question for you. Word around the local coffee table, is that using a 40% Deet insect repellent kills weeds… A producer is “experimenting” with it in his lawn and he showed me that it does work. It killed the dandelions, lambsquarters, common mallow, etc. The grass surrounding the weeds looks like it was killed too. However, my question is, will anything grow back at all after it has been sprayed with a 40% Deet?! Is it the Deet that’s killing the plant? Any thoughts, comments?
Answer: DEET, the active ingredient in most mosquito repellant will burn the foliage of most any plant and if sprayed with a heavy dose can completed desiccate even large plants. Years ago growers would spray milkweed with mosquito repellant containing DEET and it would quickly burn the plants down to the ground. Milkweed plants would soon after send up new shoots. Years ago one of the major chemical companies investigated developing DEET as a herbicide but as I recall was too expensive to manufacture and formulate and efforts to register the active ingredient was discontinued
The herbicidal action of DEET is contact and can be considered similar to any contact herbicide like paraquat, Liberty, Cobra, etc. It has limited translocation in the plant so any of the growing points not injured by the spray will develop branches and regrowth will occur. If annual plants are sufficiently covered with the spray then the plants will die but perennial plants like lawn grass, milkweed, and dandelion will grow back from perennial underground roots.
Extension Weed Specialist
Male Palmer Amaranth Plants
In the last issue of the NDSU Crop and Pest Report (#12) I included information on Palmer amaranth. In the article I indicated the following:
Below are reasons why it is being called “Satan” and why growers should quickly destroy any plants found.
#7. Female plants can grow to more than 10 feet tall with a 5-6 inch stem girth and seed heads more than 1 foot in length. Male plants are small and generally non-competitive.
My kind colleague, Dr. Dallas Peterson at Kansas State University responded that the information is not entirely accurate. His corrections are:
“I would disagree on your point about male plants being small and noncompetitive. Although male plants senesce earlier than females and typically don't grow as large late in the season, they still can be fairly large and competitive through much of the season. Attached is a picture (Photo 1) I just took with female and male Palmer amaranth side beside where both genders are well over 6 ft. tall (much taller than most wimpy ND weeds). Once the males are done shedding pollen they will quit growing, whereas the females will continue to growth in height and stem girth. Male stems usually don't get more than about 1 inch in diameter vs the females that can get to be 3 to 4 inches in diameter. A thick stand of Palmer amaranth will basically result in 100% soybean yield loss because of competition and harvest difficulties (Photo 2).
Extension Weed Specialist
Late-Season Head Diseases of Wheat
Harvesting of wheat and other small grains is starting to begin across the state, whereas some of the wheat has a few more weeks before full maturity. The relatively wide window of wheat maturity has stimulated questions on the identification and/or management of head diseases found in wheat.
Fusarium Head Blight (Scab):
Several reports of scab continue to be documented. The IPM survey scouts have reported low to moderate scab levels in most fields, with a few fields having high levels of scab (Figure 1). The ideal time to scout for scab is about a week after flowering until the heads begin to ripen. Look for prematurely bleached white florets on the head that are sometimes accompanied by an orange to salmon growth on the floret (mass of fungal spores). Stem discoloration may occur below the head as a result of the Fusarium pathogen colonizing stem tissue (Figure 2).
Ergot is often one of the most recognizable head diseases of small grains. Hard, black to purple, irregular structures (sclerotia) are seen in place of wheat kernels (Figure 3). The ergot pathogen infects the plant at flowering when cool wet weather is present. The primary management of this disease includes crop rotation, tillage to bury sclerotia and using ergot free seed. Studies have shown that fungicides are inconsistent in managing this disease.
Sooty mold is a general name given to a variety dark green to black fungi found on dead or decaying wheat heads (Figure 4). Sooty molds are often seen on heads that have been damaged by wheat stem maggot, root rots or other sources of stress that cause wheat plants to die prematurely. The presence of sooty mold is higher in years when harvest is delayed or when frequent rain events occur at the end of the growing season. Although sooty molds may discolor wheat kernels, management is not needed for this disease.
Extension Plant Pathology, Cereal Crops
Soybean Downy Mildew
We have received dozens of calls about soybean downy mildew in the last week. This is a disease that is often seen in soybeans, but generally occurs at very low levels and rarely causes economic yield loss. However, wet weather and temperatures have been favorable for disease development and we are seeing more downy mildew than normal. We are writing this article to explain what we know and what we do not know about soybean downy mildew management.
Cause. Importantly, soybean downy mildew is not caused by a fungal pathogen, but rather an oomycete pathogen, Peronospora manshurica. This is very important for management, which we explain at the bottom of the article. The pathogen is in the same group of pathogens that cause sunflower downy mildew, Phytophthora root rot of soybean and late blight of potato. Like those other pathogens, the pathogen that causes soybean downy mildew has swimming spores and needs lots of humidity/water to cause problems.
Symptoms and signs. Downy mildew initially shows up as small, pale yellow spots on the upper leaf surface (Figures 1 and 2). As the downy mildew lesions develop they may become light gray or brown and sometimes have a yellow margin. These are easily confused with other leaf spots, especially Bacterial blight and Septoria brown spot (Please refer to the previous article to help distinguish among diseases).
The key to distinguishing downy mildew is the formation of gray fungal-like tufts that develop on the underside of the leafs, directly opposite the lesions on the top side of the leaf (Figure 3).
Disease development. The downy mildew pathogen survives as thick-walled spores; these can occur on soybean debris or on seed. Once infection begins, which likely started very early this year, spores are produced on the underside of the leaves and will blow from plant to plant and from field to field. Wind driven rain will facilitate dispersal and infection. High humidity, heavy dews and temperatures from approximately 50o to 80o are favorable for disease development.
Yield loss. Downy mildew is considered a minor disease and few instances of yield loss are documented; however, yield losses of up to about 15% have been reported in rare cases. Similarly, some seed quality issues have been reported; the pathogen can cause seeds to have a slightly dull white appearance (again, rare). Unfortunately, the level at which yield and quality loss occurs is very poorly documented.
Fungicides. Here’s the tricky part…
Other crops where downy mildew pathogens are a problem (i.e. hops, grapes, cucumbers, lettuce, etc.), the disease can be managed with fungicides. However, the fungicides used target oomycete pathogens and are not generally available for soybeans; such as Revus, Zampro, Forum, Reason and Presidio. Growers who have experience with potatoes may recognize them for late blight (Phytophthora) management, and will know that these are relatively specialized products and often applied in a fungicide program approach (multiple applications).
The fungicides available in soybeans generally target the fungal pathogens. While we would not expect any of the labeled products to have excellent efficacy on soybean downy mildew, the fungicide class available that may have some efficacy are the strobilurins (Aproach, Evito, Headline, Quadris, Priaxor, etc.). Strobilurins can reduce the oomycete severity on other crops, but are often not as effective as the products we listed above. Unfortunately, virtually no data on soybean downy mildew exists and downy mildew is not listed on the label for all strobilurins. The lack of the soybean downy mildew control listed on some fungicide labels may be a result of the rarity of the disease.
Prognosis. The development of disease will depend largely on climate. If the humidity drops the downy mildew pathogen will suffer and future disease spread will likely be reduced to a dull roar.
If the humidity stays high and rainfall is consistent, downy mildew will likely continue to develop. Even in this situation though, history would suggest that that yield loss will not occur or it will be quite limited; we are fairly comfortable saying that this is the likely to be the case for the majority of soybeans in the state. However, there are some fields where severity in the mid-canopy is fairly high and if the disease spreads to the upper canopy with the same severity, yield loss may occur. However, with virtually no data about what severity level yield loss occurs at, a fungicide threshold, or efficacy data, it is very hard to provide fungicide management recommendations with any degree of confidence. We will definitely be looking to obtain some data this year and try to bridge the gap in future years.
Extension Plant Pathologist, Broad-leaf Crops
Area Extension Specialist/Cropping Systems