ISSUE 4 May 25, 2006
SMALL GRAIN DISEASE UPDATE, 5/24
Wheat streak mosaic virus was observed in a winter wheat field in Ramsey Co., by Terry Gregoire, Area Extension Specialist. As with other observations of wheat streak this year, symptoms were associated with wheat that had been planted into a field that did still had some infected volunteer winter wheat present at planting.
Tan spot was observed by Joel Ransom, Extension Agronomist, in winter wheat plots in Prosper and by Greg Endres, Area Extension Specialist, in winter wheat at Carrington. The NDSU Disease Forecasting Site (http://www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm) indicated on May 23 that most NDAWN locations did not have favorable weather the past few days for tan spot infections, because of windy, dry conditions.
Many wheat fields in states to our south are suffering from dry conditions and may not be sources of extensive inoculum of the rust pathogens.
Ext. Plant Pathologist
The following section on Ash Anthracnose is an article that first appeared in the May 29, 2003 issue of Crop and Pest Report. The information is repeated here because it is relevant:
LEAF DROP ON GREEN ASH DUE TO ASH ANTHRACNOSE
Green ash trees are losing their leaves. The seemingly healthy leaflets just drop off the trees. Ash leaves are "compound leaves", composed of (mostly) seven to nine leaflets arranged along a stalk or "rachis." In this condition, individual leaflets separate from the rachis and drop, but the leaflets appear a normal healthy green color and don't show browning or yellowing. Close examination may reveal a few tiny spots discolored brown or purple. These spots are especially noticeable on the rachis where leaflets have dropped.
This leaf drop condition is caused by a fungus disease, ash anthracnose, sometimes in combination with feeding by sucking insects. The cool, showery weather of the past several weeks favors infection by the anthracnose fungus. The cool temperatures also slow the development of the ash leaves, giving the fungus a longer time to infect. Once leaves start to fall, it is too late for any fungicide sprays to be effective because infection has already taken place.
Extreme leaf drop caused by Ash Antrhacnose
Picture taken in Grand Forks, ND, in June by Bob Stack
If you see this happening to your tree, the first thing to remember is DON'T PANIC! While unsightly and worrisome, a single defoliation by anthracnose will not permanently damage the tree. When warmer weather comes, the tree will make new leaves to replace those lost. Ash anthracnose is not a new disease; it has been recognized in the midwestern states for more than 100 years. Ash anthracnose is one of many tree diseases know to occur in periodic "boom and bust" cycles -- years when it is severe followed by years when it is rare. During the early and mid 1980s, for example, anthracnose was very common in ND, especially in the Red River valley. During that time, several studies were done at NDSU to better understand the disease and how it develops.
What to do about the problem: As mentioned, a single year of anthracnose, even if it causes severe leaf drop, will likely not permanently harm a tree. For the current season, rake up and destroy (burn, bury or compost) leaves to reduce the disease carryover. Prune-out cankered branches and remove twiggy growth to promote air movement within the crown. Fertilize trees in spring to promote vigorous growth.
If your tree(s) see repeated anthracnose damage in successive years, a preventive fungicide treatment may help. These need to be carefully timed to the bud break of the tree to be effective. A fungicide containing the active ingredient chlorothalonil can be used. Contact your county agent or the NDSU Plant Diagnostic Lab (701-231-7854) for current recommendations.
More information about ash anthracnose is available in the NDSU extension circular #PP697 "Deciduous Tree Diseases" available on the web at:
Kasia Kinzer, with NDSU Plant Diagnostic Lab, adds that conditions for development of ash anthracnose were favorable for the first couple of weeks in May, when weather was cool with prolonged moisture. Ash anthracnose lesions can be seen on the leaflets, either as the type of blotches that deform the leaflets (see image below) or as distinct, round, purplish brown leaf spots (this type probably didn’t develop into blotches because the environment may not have been favorable). Ash anthracnose has been prevalent for the past three years, so protecting smaller trees with the fungicide applications described above may be beneficial in early spring 2007 if those trees have suffered defoliation due to ash anthracnose in 3 out of 5 consecutive years. For this year, if you missed the critical timing recommended for the first fungicide application, some studies suggest that a fungicide application applied after the critical window of time may still benefit affected trees by reducing late-season infections.
Blotches caused by Ash Anthracnose
that lead to deformed leaflets
Picture taken May 23, 2006 from an ash tree near
Waldron Hall on the NDSU campus in Fargo, ND
For most trees, applying fertilizer and watering sufficiently to encourage vigorous re-growth of defoliated trees may be the only ‘treatments’ required for this disease. You can read more about this and other diseases of trees at the following web sites:
NDSU Plant Pathology
NEW DIAGNOSTIC LAB PERSONNEL
The lab has hired a new, temporary summer receptionist, Ms. Aimee Thapa, who some of you might remember as Aimee Stockman. Ms. Thapa finished her Bachelor’s degree in Horticulture Science (with a minor in business) from NDSU earlier this month.
An assistant diagnostician, Ms. Febina Matthew, will also spend a few hours per week in the lab, particularly to help process soybean samples. Ms. Matthew finished her Master’s degree in plant pathology in April, and we look forward to having her in the lab this summer.
Of course, even under a well-staffed situation, turnaround time depends largely on the type of sample submitted and the suspected pathogen or other disorder involved. Whenever you submit a sample to the lab, please feel free to call or email with questions on the status of your sample.
PLANT DIAGNOSTIC LAB UPDATE
Wheat streak mosaic virus was confirmed on a wheat sample from north central North Dakota submitted to the lab last week. Tan spot symptoms were observed on a wheat sample submitted. A spruce sample was diagnosed with an abiotic problem – probably over-watering. A cottonwood sample has an unidentified leaf blotch that may be due to an abiotic (non-pathogenic) factor. Several turf grass samples remain under evaluation, including a bentgrass sample from a golf green that is suspected to be infected with a Pythium disease (no other pathogen was detected).
Home mold inquiries continue to reach the lab, and typically, about 30 mold samples are evaluated each year. To a limited extent, we can evaluate samples with suspected mold contamination. We cannot inspect dwellings or take air-quality samples.
Two inquiries in the past month were related not to home mold, but to a phenomon of concrete known as efflorescence. The efflorescence was described by the individuals as white, fluffy, and crystalline. Efflorescence is a deposit that can occur on bricks, concrete, and other masonry in general. It seems it occurs as water or hydrostatic pressure moves through the concrete. The salts may be sodium sulphate, potassium sulphate, sodium carbonate, calcium sulphate, sodium bicarbonate, calcium carbonate, sodium silicate, magnesium sulphate, or others. The efflorescence is usually somewhat water soluble, so a good wash with soapy water may be all that is needed to clean up the unsightly white ‘growth’. An acid, such as vinegar, might be needed to help dissolve the substance away.
NDSU Plant Diagnostic Lab
206 Waldron Hall, PO Box 5012
Fargo, North Dakota 58105