May 22, 2017
Identify and Control Diseases In Season
Your best defense against yield-robbing diseases is planting varieties that have excellent disease resistance packages. Still, recommended varieties often don’t have tolerance against all diseases. Equally challenging, diseases can change frequently with different strains or races, leaving your crops susceptible. That’s not to mention the uncontrollable weather conditions that can increase the severity and reach of these diseases. To more effectively manage diseases in season, proper scouting, early identification and quick action are all best practices, as well as working with your trusted adviser to select the best control options for your farm and varieties.
Read on to learn how you can spot—and help control—some of the most common diseases that may be problematic this season. Background
While most commonly found on the leaf’s surface, Leaf Rust can also appear on the sheath, as identified by the reddish-brown pustules that develop and leave a rust-colored residue upon contact. Because these pustules can be as small as an 1/8 inch in length, you’ll need to inspect leaves closely to spot the disease. Keep in mind, varieties with a stronger level of resistance will feature even smaller pustules that may be more difficult to spot. In all cases, Leaf Rust prefers temperatures around 65 to 80 degrees.
Timely application of foliar fungicides is the most effective way to help control Leaf Rust for varieties without built-in resistance. To determine the need for fungicide as well as best timing, growers should follow wheat reports from regions to the south of them where the disease will likely start earlier.
Yellow (Stripe) Rust
Yellow (Stripe) Rust is characterized by its yellow or orange pustules that appear on the leaves. These pustules can be seen in rows generally after stem elongation in wheat. Yellow (Stripe) Rust is more prominent in cooler conditions, earlier in the season when it’s around 50 to 65 degrees. When temperatures rise above 80 degrees, Yellow (Stripe) Rust development will generally cease or be severely restricted.
While many varieties have proven resistance against Yellow (Stripe) Rust in past seasons, it is still important to remain vigilant when scouting for the disease because of the likelihood of new races arising. It’s also vital to keep in mind that many varieties only have resistance following the reproductive stage, so infection prior to the jointing stage can have major consequences on yield. Timely fungicide applications can help control the disease and decrease potential yield loss. When applying fungicide, it’s best to wait until after the flag leaf is at least 50 percent emerged (but prior to the initiation of flowering). You should choose the fungicide that best fits the disease present and the conditions in the field.
Septoria Leaf Blotch
Septoria Leaf Blotch is a widespread foliar disease that can affect your wheat yields. It’s characterized by necrotic lesions found on leaves or stems and is more prevalent in cool, wet weather. The first visible symptom of Septoria Leaf Blotch is the small, light-green or yellow spots that appear between the veins of the lower leaves soon after seedlings emerge. While small, these areas can rapidly expand into light-brown lesions, often surrounded by a yellowish circle. In many cases, this disease can accompany Stagonospora Glume Blotch, which is also very common in rainy years. When both pathogens occur together, they’re known collectively as the Septoria Blotch Complex.
While crop rotation can help alleviate the disease, additional steps can be taken before and during the season to help manage Septoria Leaf Blotch. Avoiding excessive nitrogen levels and maintaining a proper seeding rate can help create a more spacious canopy, reducing favorable conditions for the disease. During the season, it’s important to protect the flag leaf with a foliar fungicide treatment, as well as to continuously monitor the crop through scouting.
Plants affected by Powdery Mildew will display white powder-like spots on the leaves and stem—it will look a little like spilled flour. Typically, the upper surfaces of the lower leaves are the most affected areas, though symptoms may appear on any part of the plant that is above the ground. Symptoms are visible early in the season and can be particularly prevalent during cool, wet conditions. As the weather grows warmer and drier, Powdery Mildew will usually fade out, leaving plants affected at the lower leaves in little danger of yield loss. However, if cool and wet conditions persist throughout the season, the entire leaf can turn yellow and die, reducing the plant’s yield potential for the season. This is most often the case in fields with dense stands and high nitrogen fertility.
To help protect your field against Powdery Mildew and reduce your potential for yield loss, choose the fungicide that best fits the conditions in your field, and be sure to apply after flag leaf emergence. If fungicides are applied too soon, plants may be left unprotected later in the season.
Barley Yellow Dwarf Virus (BYDV)
Barley Yellow Dwarf Virus (BYDV) is most often identified by a general yellowing of the leaves, sometimes accompanied by additional colors—including purple, red and orange—as well as dwarfing of the plant. Discoloring will occur from the tip to the base and from the leaf margin to the midrib of the leaf. These symptoms can often be mistaken for nutritional issues or frost damage.
To help prevent BYDV, consider using a seed treatment with insecticide to control the vector of the disease, Bird Cherry Oat Aphids. Planting later in the season can also help you avoid aphids. Aphids should be identified by scouting early in the season, but it’s worth noting that not all aphid species vector BYDV. Keep in mind that beneficial insects are effective at controlling smaller populations of aphids, so if insecticides are used as a method of control, you will also harm the beneficial insect population if they are present in the area.