By Kaeley Kindrachuk, AT, Crops Extension Specialist, Outlook and Joel Peru, PAg, CCA, Irrigation Agrologist, Outlook
The last several years have been conducive for plant disease development in field crops. Combine that with irrigation in the Outlook area, and there is a perfect scenario for disease development that may warrant fungicide application. However, the warm, windy conditions this spring, along with the lack of moisture, have made it very difficult to find disease in fields - even in the Irrigation Crop Diversification Corporation (ICDC) plots under irrigation.
Despite the lack of disease, we invited our Provincial Plant Disease Specialist, Barb Ziesman, to Outlook to discuss plant diseases. Our crop walk featured several different crop types, including peas, dry beans, canola, wheat, flax and lentils. Even though it was difficult to find disease, and even impossible in some plots, we had a good discussion on disease identification, risk assessment and management.
Our first stop was the pea plots at the ICDC off site station (pea plots one and pea plots two). Given the conditions, we were able to see the start of mycosphaerella blight on the lower leaves. Mycosphaerella blight is usually a residue-borne disease that will first be found on the lower leaves of pea plants. This disease requires regular scouting, as it can progress up the plant. The risk for yield loss increases if the disease progresses into the crop canopy. We also saw evidence of root rots in the pea plots (yellowing of lower leaves), but, due to the plots being needed for yield, we were unable to pull any plants to observe any discoloration and pinching off on the stems (Photo 1).
Our second stop was the dry beans (dry beans one, dry beans two and dry beans three). Dry beans are the most common pulse crop grown under irrigation in the Lake Diefenbaker area, but there are some grown under dryland conditions around the province. In the dry bean plots, we saw some early stages of bacterial blight. Early stages of bacterial blight look like yellow spots or even water-soaked spots that appear on the lower leaves. Bacterial blight is caused by bacteria, so the registered fungicides will not have an effect on this, as they are only effective for fungi infections. Also in the dry beans, we saw root rot in the lower areas of the plots. Plants affected by root rot were stunted. When pulled, the roots were pinched and had a reddish-brown discoloration. Without being in a lab, we weren’t able to narrow down exactly which pathogen we were seeing, but likely the root rot was caused by a complex of multiple pathogens. We don’t have any fungicides registered for root rots, but we can help prevent infection by planting disease-free seed that has been tested. We can also use seed treatments to protect against Fusarium, Pythium and Rhizoctonia (some of the common root rot pathogens). These root rots can infect most crops.
Our third stop was a very dry, irrigated canola plot (canola plot one and canola plot two). We were able to walk through the plot and come out with dry pants; however, we did notice a couple of leaves that had petals stuck to them. This tells us that if the plots were wet and the petals were falling on the leaves, it could lead to the development of sclerotinia stem rot. This plot was past the recommended sclerotinia stem rot fungicide application window of 20 to 50 per cent bloom. We also talked about blackleg at this stop, even though we didn’t see any. There are two different times we can scout for blackleg; the first is early in the spring, on cotyledons or on the first couple of leaves. Early infection will cause the highest yield loss and lead to basal cankers and darkening of the internal stem tissue (pith). The second time we can scout for blackleg is later in the year during swathing or harvest. Pull plants and cut the stem where the plant meets the ground and check for blackening in the stem (Photo 2). This is also a good time to be checking roots of canola plants for clubroot. Be on the lookout for galls, which will be forming on the lateral roots if the disease is present at low levels (Photo 3). If clubroot is found at high levels, there will be galls forming on the tap root. Clubroot is easier to manage when it is found at low levels, so diligence in scouting is necessary.
The next stop was at the cereal variety trials (cereal varieties one, cereal varieties two and cereal varieties three). The first thing we noticed was some white heads in a few of the plants. White heads can be caused by several different things: wheat stem maggot, moisture stress or root rot. It’s important to take a look at the plants if you do see white heads in your fields. We did not see any leaf diseases in these plots, but, when scouting for leaf diseases, start scouting early in the season and watch for disease progression. It is most common to see leaf diseases start at the bottom of the plant, but the only thing we saw was natural die off.
Barb also explained the difference between monocyclic and polycyclic diseases. Polycyclic diseases have more than one disease cycle per year. We need to continually monitor these diseases. Polycyclic diseases include cereal leaf diseases, ascochyta blight, anthracnose in lentils, and mycosphaerella blight in peas. Monocyclic diseases have one disease cycle per year. For these diseases, we need to scout for the conditions that favour the disease, not disease symptoms. Monocyclic diseases include fusarium head blight and sclerotinia stem rot.
The flax plots came up short with providing us disease to look at, but Barb did discuss how to scout for pasmo, which is the most prevalent disease found in flax (flax one and flax two). Pasmo will start lower on the plant and progress up the plant with a characteristic brown banding pattern seen later in the season (Photo 4).
The lentils also were free from disease, but Barb did a great job of describing what anthracnose, ascochyta blight, sclerotinia white mould, botrytis gray mould, and stemphylium blight will look like if the environment is conducive to disease development (lentils one and lentils two).
The boot covers that we were wearing can be found in a variety of styles at U-Line or VetSource Canada. Join us for the next crop walk on July 25 live from Crop Diagnostic School in Melfort on the Saskatchewan Agriculture Facebook page or the ICDC Twitter account.
More information on plant diseases can be found by visiting the Saskatchewan Pulse Growers website, the Sask Wheat website or clubroot.ca.