ISSUE 10 July 9, 1998
CRISIS EXEMPTION FOR RONILAN ON CANOLA
As Indicated last week, a crisis exemption was declared in North Dakota and Minnesota for the use of Ronilan to suppress Sclerotinia on canola. The North Dakota crisis was declared on July 1, and runs through July 16. EPA was approached shortly after the Quadris section 18 was granted due to short supply of Quadris, the fact that many fields were past 30% bloom and Ronilan could be applied up to 50% bloom, as well as to cost considerations.
Two formulations of Ronilan have been shipped into Fargo for distribution in both Minnesota and North Dakota: Ronilan EG and Ronilan DF. Both are 50% active ingredient and have identical use labels.
The section 18 label indicates that it is recommended that Ronilan be applied at 20-50% bloom. "This will normally be about 4-8 days after the beginning of flowering." Based on a Canadian growth stage guide produced by the manufacturer, BASF, 50% flowering is when the lower pods are elongating but there is still a cluster of buds at the tip of the main stem. The section 18 label states "a maximum of 1 pound of Ronilan per acre per application may be used." Use is limited to one application per season.
Information from a BASF Canadian brochure provides research data from Canadian government and university trials. Percent control in the trials was 72% when applied at 20-30% bloom, 77% when applied at 30-40% bloom, 87% when applied at 40-50% bloom and only 48% when applied at 60-70% bloom. Thus, although Ronilan was most effective when applied at 40-50% bloom, it is essential that it be applied before 60% bloom, as efficacy is greatly reduced at that time. Reference to the BASF growth stage brochure indicates that at 60% bloom, there are pods about 2/3 of the way up the main stem and few or no buds at the tip of the main stem.
The Canadian label rate is 0.3-0.4 Kg/A, which converts to 0.66-0.88 lb/A. The statement of "a maximum of 1 pound" on the section 18 label may be a rough conversion of the 0.4 Kg/A rate, which is 1 Kg/Ha.
Ronilan is a contact fungicide. It has about 36 hours of post-infection ("kick-back") activity.
Again, a thank you to all who helped make both the Quadris and the Ronilan section 18s a reality.
SECTION 18 FOR TILT ON DRY BEANS
On July 2 The Environmental Protection Agency (EPA) granted a section 18 for the use of Tilt on dry beans for rust control. Tilt is to be broadcast applied (ground or aerial) at 4 fl oz/A. A maximum of 3 applications are allowed. There is a 28-day preharvest interval and a 7-day grazing or forage feeding interval.
Tilt is locally systemic, provides 14 days protection and has 4 days of post-infection activity. Producers should plan to use Tilt as a preventive rather than a curative. Frequent curative use could lead to the development of resistance; using Tilt as a protectant is an example of good stewardship and resistance management.
WHITE MOLD MANAGEMENT IN DRY BEANS
There have been several calls recently reporting that dry beans are flowering but that they are small and not forming a canopy. Questions are whether to wait to spray and whether some of the newer varieties may not need a white mold spray.
There are no easy answers to either of these questions. Some of the newer varieties are less susceptible to white mold, but I would not call them resistant. See Circular A-654, North Dakota Dry Bean Performance Testing, 1997, for a summary of disease reactions (in the back) and for white mold ratings from several trials. This will help evaluate the need for a fungicide. However, when white mold pressure is high, I believe that most varieties would respond to the use of a fungicide.
As to the lack of a canopy, this can make a great difference when conditions are marginal for white mold development. When conditions are extremely favorable, so that the plants remain wet with or without a canopy, then the lack of canopy is not very significant. Weather at the beginning of this week was the type that favors infection with or without a canopy.
Extension Plant Pathologist
SMALL GRAIN DISEASE UPDATE
The big story in small grains in eastern North Dakota this week is the big increase in drowned-out acres, evident last week but increasingly apparent with the recent rains over the weekend. Large white patches are seen along the drainage ditches and low spots of the fields. With standing water in many fields, these areas are only going to get bigger. Other areas of the state with a lot of rain may see drown-out in the near future, or increases in leaf and head diseases.
Scab: Beyond the drowned-out spots, most spring wheat fields examined yesterday and today are holding their own against scab! Much of the crop surveyed in EC North Dakota was in the late milk to early soft dough stage of kernel development. Scab incidence averaged around 10% and severity averaged from 7-14%, giving a field severity of still only 1% or less. This level is an increase over that seen last week, but still is a fairly low level. Some of these fields may have been sprayed with a fungicide, but fields surveyed were chosen at random and treatment history was unknown.
Incidence of scab is higher in barley fields surveyed, with 30% incidence common in Cass, Cavalier, and Pembina counties. However, with only 2 kernels per head showing infection, the severities of scab in barley averaged 3% and total field severities in barley were also about 1%. Time will tell if this relatively low level may still result in quality problems that prevents the barley from grading as malting.
Fungicide spraying of wheat in past years has reduced the field severity of scab by 40-60%. Growers who used fungicides must remember that 100% control has NOT been achieved, and they will still see some of this disease, even in treated areas, if conditions are right for infection. Our 1998 fungicide trials have not been evaluated yet for % control.
Leaf diseases are increasing in wheat fields, and some infections of tan spot, Septoria, and leaf rust are seen on the flag leaves now. If more than 5% of the flag leaf is already infected, it is too late to apply fungicides. With 5% of the leaf area already showing symptoms, it is most likely that additional infections have occurred which are not yet visible. Systemic fungicides have some "kick-back" activity against very new infections, but once the fungus is well established in the leaf, the fungicides cannot protect or cure that diseased tissue.
Where fungicides have been used this year prior to infection of the flag leaf, the leaves are noticeably greener than in untreated areas. In a few fields where Septoria infections are severe and moving up to the flag leaf, some early symptoms of Septoria glume blotch are also apparent. Glume blotch starts at the tip of the glume and usually causes a greyish brown discoloration from the tip to about half-way down the glume. The tiny, black fruiting bodies of the fungus also are usually seen in the glume lesion. Fungicides applied to control scab and leaf diseases will also help prevent glume blotch.
Fungicides will NOT prevent bacterial diseases such as bacterial leaf lesions or bacterial black chaff on the head. In surveying fields today in Cass Co., patches of bacterial infections were very evident in a field of Russ HRS wheat, with the leaves showing shiny brown lesions running parallel to the leaf blade. The awns and some stems also showed brown discoloration due to bacterial infection, giving the patchy area a general brown to bronze coloration. The characteristic brown-black streaks of bacterial black chaff were also apparent on the glumes. Bacterial black chaff and leaf blight often occurs in patches in a field were swirling winds have caused soil particles to make tiny wounds in the plant tissue, wounds that are sites of entry of the bacteria.
FUNGICIDES AND RAINFASTNESS
Eighty percent of locally systemic fungicides (Tilt, Folicur, and Benlate) are absorbed by the plant within the first hour after application. The remaining fungicide is absorbed in time and the optimum rainfastness is reached at 4 hours after application. Re-treating the field is not needed if it rains 1.5 to 2 hours after applying these fungicides.
Protectant fungicides (mancozeb such as Dithane) are readily washed off the plant if a substantial or heavy rain occurs within 8 hours after application. Re-treating the field may be required for maximum plant protection.
Leaf rust questions still arise from various locations in the state. If leaf rust severity on small grain's flagleaf is 5% or less, applying a locally systemic fungicide may help protect the flagleaf from further infection. However, if the leaf rust severity on the flagleaf is greater than 5%, it is too late to spray fungicides. Additional infection has occurred and you are unable to see the symptoms from the "hidden" infection sites.
For example, if you see 5% leaf rust severity on the flagleaf today, an additional 10 to 20% severity may apperar in another 2 to 3 days from the "hidden" sites. The fungicides are unable to counteract the infection. Fungicide applications are now too late to spray for both disease control and economic advantages.
Area Extension Specialist Crop Protection
PLANT DIAGNOSTIC LAB REPORT
The tide seems to be shifting from evergreen trees to hardwoods in the lab. The early season evergreen diseases and abiotic disorders are being replaced by maples, many of which are being affected by another eriophyid mite. It is commonly called maple bladder gall mite, or Vasates quadripedes. This mite species produces irregularly rounded galls on the leaves. There are usually several galls produced in groups on the leaves, greenish in color and gradually becoming bright red. These gall producing mites dont require treatment as they very rarely cause damage to the tree. It is best to simply enjoy this natural phenomenon knowing that the tree wont be permanently injured and the symptoms wont usually last through the summer. If they are just too unsightly for you, however, they can be treated with compounds such as Sevin, malathion, Kelthane or dormant oils. As always, be sure to follow label recommendations when applying any type of pesticide.
There have been a few sunflower samples submitted to the lab with a condition that results in a stem snap. This occurs when periods of warm weather follow a cooler temperatures. Plant growth slows as the temperatures cool and then increase again as temperatures warm up. Development of structural support tissues, however, doesnt always keep up with the rapid growth induced by warmer temperatures. As the weight of the top of the plant increases, the stem snaps and the plants lodge.