ISSUE 9 July 2, 1998
PLANT DIAGNOSTIC LAB REPORT
The recent fairly wet weather that parts of the state have been experiencing has been quite favorable for development of several fungal diseases and now that the crops are maturing, some of the diseases are starting to manifest symptoms. We are still seeing sugarbeet samples suspected for Aphanomyces, but the leaf diseases are starting to show up as well. All that we have confirmed in the lab is bacterial leaf spot, caused by Pseudomonas syringae. This disease is rarely an economic threat but can be confused with Cercospora leaf spot which is an important and potentially destructive disease. These 2 disease can usually be easily distinguishable in the lab for confirmation. There have been 5 potato samples submitted for late blight testing. None of them were positive but the disease has been confirmed in the Red River Valley. The dry bean samples that have been submitted all have root rot infections, Fusarium and Rhizoctonia. There were 2 sunflowers submitted showing symptoms of stem snap, a condition that arises when a period of warm weather follows a long period of cooler weather. The plants grow too fast for the structural support tissues to keep up and the weight of the plant causes the stalk to snap near the bottom.
On the horticultural side, signs of dutch elm disease (DED) are beginning to show up. Although it is fairly widespread in North Dakota, there are still parts of the state that have not reported this disease. The most common symptom is wilting, yellowing and dying of parts of the canopy of the tree. This disease is vectored, or transmitted, by 2 different species of beetles, and also through root grafts. Trees within approximately 25 feet of each other may spread the disease from one to another. This is a fungal disease but once a tree is infected, there is usually nothing that can be done to save it. The best management for this disease is a proactive program that prevents the spread of DED. Some of the strategies to employ in this program include preventing root grafts by trenching between trees and community wide sanitation plans that include destruction of dead and dying elms, and destroying or debarking elm firewood immediately (it harbors the beetles that transmit the fungus). Insecticides for control of the beetles and injections of preventive fungicides have also proven to be effective to some degree. If you suspect this disease is affecting your tree or any tree, alert your city forester or county agent. You may also submit a sample directly to the lab. Samples should be at least 1 inch in diameter, 6-8 in length, and come from an affected area of the tree to recover the pathogen and confirm the presence of the disease.
TIMING LIMITS WITH POST HERBICIDES FOR CORN
Recent weather has hampered timely post_emergence herbicide application in corn. Effectiveness of late-season weed control may be reduced but still necessary. The following is the maximum corn size allowed on herbicide labels.
Accent = Up to 20-inches tall with 6 or fewer collars; apply with drop nozzles at 20-to 36-inch height.
Accent + atrazine = Up to 12-inches tall.
Accent + Banvel/Clarity = Up to 8-inches tall; apply with drop nozzles at 8- to 24-inch height.
Accent + bromoxynil = Up to 20-inches tall with 6 or fewer collars; apply with drop nozzles from 20-to 24-inch height.
Accent + Hornet = Up to 20-inches tall with 6 or fewer collars; apply with drop nozzles at 20- to 24-inch height.
Accent + Scorpion III = Up to 8-inches tall; apply with drop nozzles at 8- to 24-inch height.
Accent Gold = Up to 20-inches tall with 6 or fewer collars; apply with drop nozzles at 20- to 24-inch height.
Atrazine = Up to 12 inches tall.
Banvel = spike to 8-inches tall; 8- to 36-inches tall or 15 days prior to tassel with directed spray.
Basagran = Not specified.
Basis = spike to 4-leaf (2 collar) (V2).
Basis Gold = Up to 12-inches tall and prior to 6-collars.
Beacon = Up to 20 inches tall.
Bladex/Cy-Pro = Up to 5-leaf stage.
Bromoxynil = prior to tasseling.
Clarity = spike to 8-inches tall.
Hornet = Up to 24-inches tall.
Laddok = Up to 12 inches tall
Liberty = Up to 24 inches tall or 7 collars (V7) (Liberty Link corn only).
Lightning = up to 12 inches tall (Imi corn only).
Permit = Up to 36-inches tall; drop nozzles must be used at 24- to 36-inch height.
Scorpion III = Up to 8-inches tall.
Stinger = Up to 24-inches tall.
Sencor + broadleaf herbicide = prior to tassel.
Shotgun = Up tp 8 inches tall.
Tough = Up to 68 days prior to harvest.
2,4-D = Up to 8 inches tall. Use drop nozzles when corn is over 8-inches tall but before tasseling.
Spray boom height should be raised during application to avoid concentrating the herbicide over the corn row. Refer to labels and the NDSU Extension Service 1998 Weed Control Guide for additional details on herbicide use.
NEW SMALL GRAIN INJURY SYMPTOM GUIDE
North Dakota and Minnesota Extension Service has produced a new publication showing herbicide and non-herbicide injury symptoms on small grains.
The new publication, "Herbicide and Non-herbicide Injury Symptoms on Spring Wheat and Barley," BU-6967-S (MN) or W-1141 (ND) is patterned similar to NCR 377, Herbicide Mode of Action and Injury Symptoms, except herbicide mode of action groupings are listed in alphabetical order and a section on non-herbicide symptoms was added.
The guide is available to help individuals determine the cause of injury on wheat and barley. It contains pictures showing injury symptoms caused by various classes of herbicides (imidazolinones, sulfonylureas, etc.) through misapplication, drift or tank contamination. The guide is arranged by mode of action and gives information on proper herbicide application timing, and describes herbicide injury symptoms on wheat and barley through herbicide mode of action, application method, and selectivity.
The second part of the guide shows pictures and describes several non-herbicide injury symptoms on spring wheat and barley. Injury symptoms are grouped by cultural practices, environmental factors, fungal diseases, insect damage, nutrient deficiencies, soil pH, and viral diseases.
These guides will be useful for classroom or extension audiences.
The guide is a joint publication of the North Dakota State University Extension Service and the Minnesota Extension Service. Copies can be ordered at a cost of $3.50 + S&H from:
North Dakota State University Extension Service
University of MN Extension Service
SPRAYER CLEANING SOLUTIONS FOR HERBICIDES
Sprayer contamination is an increasing concern as crop rotations become more diverse and associated herbicides uses require frequent changes in the same equipment. An excellent reference, Cleaning Field Sprayers to Avoid Crop Injury, G 4852 published at the University of Missouri outlines the steps in sprayer cleanup for each herbicide group. It also includes a summary of recommended cleaning solution.
The publication can be ordered from Extension Publications/Distribution Center, University of Missouri, 2800 Maguire Blvd., Columbia, MO 65211. (573) 882-7216. Cost is $0.75 + $0.12 sales tax + $1 S&H with a total of $1.89 per copy.
The chart below summarizes the cleaning agents for several herbicides.
Ammonia + water:
Kerosine or diesel fuel followed by ammonia + water:
Ammonia or commercial tank cleaner + water:
|Blazer||Buctril + Atra||Buctril||Classic|
|Dual Magnum||Flexstar||Fusilade DX||Fusion|
Detergent + water:
Commercial tank cleaner + water:
Detergent or commercial tank cleaner + water:
Ammonia, commercial tank cleaner, or detergent + water:
ADJUVANT USE IN LOW GALLONAGE SPRAY VOLUMES
Extended wet weather has forced herbicides to be applied by aerial application rather than by ground sprayer. A question asked is if adjuvant rates should be adjusted for low sprayer volumes. For example, some oil adjuvants are applied with Accent, Raptor Pursuit, Assure II, and other POST herbicides at 1% v/v or 1 gal/100 gal water. At 15 to 20 GPA, 1% oil adjuvant would provide adequate adjuvant load. However, in aerial applications at 5 GPA, 1% v/v may not provide enough adjuvant for the herbicide.
Some herbicide labels contain information on adjuvant rates for different spray volumes. For example, Pursuit and Raptor label requires oil adjuvants to be added at 1.25% v/v or 1.25 gal/100 gal water for aerial application (5 GPA). Additional recommendations to assure sufficient adjuvant load would be to keep the adjuvant rate on an area basis. For example, instead of using oil adjuvants at 1% v/v, apply the adjuvant at 1.5 to 2 pt/A to insure adequate load at all spray volumes. The information above applies specifically to oil adjuvants and is based on limited field research. Surfactant rates of 0.25 % v/v or 1 qt/100 gal water is sufficient across water volumes.
Quad 7 applied with Accent, Pursuit, and Raptor may help simplify the confusion. Quad 7 is recommeded at 1% v/v regardless of spray volume. Data indicates Quad 7 at 1% v/v from 5 to 20 GPA will provide necessary adjuvant enhancement for similar weed control at all these spray volumes with Accent.
NDSU Extension Weed Specialist