PHYLLACHORA MAYDIS: YES, THAT WOULD BE TAR SPOT
Recently, tar spot has been a concern in terms of corn foliar diseases. It is a new-comer having been first been identified in 2015. Actually, some credit can be attributed to a former Dairyland Seed agronomist for getting the first official confirmation of tar spot in Indiana.
In 2021, tar spot is again getting some attention. It has shown up a little earlier than in the last few years. Reports were as early as the second week of July.
What to look for? As the name suggests, the first clue is tar-like flecking or lesions on the leaf surface. The “tar spots” are raised lesions and typically can’t be rubbed off as is the case with rust pustules. Conditions favoring the disease tend to include higher humidity and/or leaf wetness. Indications are that it may prefer modest temperatures as opposed to extremely high temperatures.
The two big criteria for control are growth stage of the corn and advancement of the disease. In a sense, it’s a race to the finish line. Can the corn progress to maturity faster than the disease can compromise the functioning leaf tissue? Early infestations that take large leaf areas can rob yield 20 to 60 bushels according to some experts.
Fungicides are now known to aid in the control of this leaf pest. Thus, timely application of an appropriate fungicide may be warranted in certain instances. Crop rotation can be useful as it is now known that the disease can overwinter on crop residue. In addition, now that we have a couple years of tar spot experience, we have a better understanding on hybrid selection against this disease.
SOYBEAN DISEASE UPDATE
The Dairyland Agronomy Team has noticed the start of some soybean diseases showing up in certain areas. Most of the soybean crop across the Dairyland footprint is in the mid-pod filling stage and the weather has been conducive for disease development. A few of the common diseases that are popping up include Sudden Death Syndrome, Brown Stem Rot and White Mold.
Sudden Death Syndrome
Sudden Death Syndrome (SDS) is caused by the fungus Fusarium virguliforme and infection occurs in early spring. Disease symptoms don’t usually appear until around August. This is because rain during the reproductive stage can cause the disease to start producing toxins which can kill the leaves. SDS tends to favor early planted soybeans, cool damp soils and compacted soils. The other factor common with SDS is Soybean Cyst Nematode (SCN). The SDS organism overwinters in the soil, in crop residue and in the soybean cyst which is why there is a close association between SCN and SDS. Losses from SDS range from minimal to, in some cases, severe.
The first noticeable SDS symptoms are chlorotic blotches that form between the veins of the soybean leaflets, which expands and turns necrotic. Those leaves will die and can drop off, leaving only the leaf petiole. The final diagnosis includes splitting the stem to look for discolored stem cortex. The cortex will have a light brown discoloration while the pith will remain white. Brown stem rot (BSR) can have similar leaf symptomology but will have a brown discolored pith when the stem is split.
Controlling SDS after infection is not possible so prevention is key. Keep accurate records of problem fields and varieties. Planting problem fields later in the spring and eliminating soil compaction can also help in reducing the incidence of SDS. Selecting soybean varieties tolerant to SDS and containing SCN, along with using seed treatments like ILeVO® will help control SDS and SCN.
Brown Stem Rot
Similar to SDS, the soilborne fungi that causes Brown Stem Rot (BSR) infects early in the spring and symptoms don’t usually show up until the soybean is in reproductive stages. BSR is caused by the fungus Phialophora gregata which infects the plant through the roots and then grows inside the vascular tissue. There are two different genotypes of the fungus that causes BSR. Type A causes leaf and stem symptoms and is more aggressive. Type B typically only causes stem symptoms and is less aggressive.
Symptoms usually appear around the R3-R4 growth stages and are favored by cooler temperatures and adequate moisture. Foliar symptoms can appear similar to SDS with interveinal chlorosis that turns necrotic. BSR will have a brown discolored pith that extends from the lower stem upward, while SDS will have a white pith.
BSR cannot be controlled once the plants have been infected. Soybean cyst nematode is also known to contribute to BSR infection so selecting a variety that has SCN resistance along with BSR tolerance will be key in helping to prevent BSR in future years. Other management practices include rotating away from susceptible crops for two or more years and using tillage to incorporate plant residue.
White Mold, Sclerotinia sclerotiorum, primarily infects the soybean plant through the flowers. Humid conditions coupled with rain and moderate temperatures during soybean flowering are conducive for white mold infection. This fungus can survive in the soil as sclerotia for several years so management is important. Fungicides are effective against white mold if applied around the R1-R3 growth stage. Other management practices include lower planting populations, wide row spacing, crop rotation and tillage.
Foliar symptoms are interveinal coloring of grey-green and can resemble other soybean diseases such as brown stem rot or stem canker. Symptoms usually appear in soybeans between the R3 and R6 growth stage. Fluffy white mycelium growth can be found on the stems near the nodes. Leaves of infected plants eventually die but remain attached to the stem.
SILAGE PLOT HARVESTING AND SAMPLING PROTOCOL
Corn Silage harvest season is quickly approaching, and for those in the drought-stricken West it is already here. Take a minute to read through this list to be sure you’re ready to go when the time comes. Just a reminder that NO data is better than BAD data.
i. Harvest date
ii. Grower name
iii. DSM name and/or number
iv. Hybrid name
Sampling Procedure - for each individual hybrid:
Rock River Laboratory
710 Commerce Drive
Watertown, WI 53094
Thank you to all of our plot cooperators for your hard work this growing season. We appreciate your time and effort to help our team gather valuable information on the Dairyland Seed portfolio of products. Stay safe!
SHOW OFF YOUR FIELDS WITH DAIRYLAND SEED FIELD SIGNS
Signing your fields is a great way to promote Dairyland Seed products in your area. Field signs for corn, soybeans and alfalfa can be ordered by calling the Dairyland Seed headquarters at 800-236-0163 and ask to speak with Stacy Hendricks or Rita Frank.
CORTEVA TECHNOLOGY USE AGREEMENTS
All growers with orders for any Corteva Agriscience brand seed product, regardless of crop or trait (including non-GMO products) need to have a signed Corteva Technology Use Agreement in place by September 1. Growers should sign the Corteva Technology Use Agreement electronically at www.agcelerate.com. Signing electronically is preferable, however, paper copies are available at www.traitstewardship.com or by calling Rita Frank in the Dairyland Seed West Bend office at 800-236-0163.