Tank Mixing Insecticides &
Fungicides in Sugarbeet – August 3, 2006
There have been questions about tank mixing insecticides (for lygus and grasshoppers) with fungicides. It’s best to exercise caution when trying this, always check the label and information sources to see if there are any reported incompatibility issues. Given current economic factors, there is significant motivation (especially this summer) to double up applications. But the economic advantages may be overcome by losses if the technique is used incorrectly. Things to consider:
Mechanical compatibility – make sure the application methods are compatible for both chemistries (calibration, water, pressure, nozzles, agitation, carriers, etc). Applying a pesticide using inappropriate application methods may seriously impair the efficacy of the chemistry and not produce the desired results.
Physical compatibility – it’s generally a good practice to perform a jar test (see below) to check for physical compatibility of chemistries prior to tank mixing. With the increased frequency of tank mixing, most of us have witnessed the formation of nasty, stringy precipitates (or as some call it, ‘chem snot’) that can clog lines and screens. Frequently this is a result of the formulation rather than the active ingredients. The photos show how a change in formulation can make a big difference in physical compatibility. Pic #1 is an original formulation of a synthetic pyrethroid insecticide that had significant precipitation problems when mixed with 10-34-0 starter fertilizer. Pic #2 shows the newer formulation of the same product with a much improved ability to tank mix (thanks to Mark Boetel from NDSU for the photos).
Chemical compatibility –
chemical antagonism may lead to the loss of effectiveness of one or both
pesticides. Perhaps the more
commonly encountered chemical incompatibility is phytotoxicity. When tank mixing full
rates of pesticides, there is not only the full rate of a.i.
for both pesticides in the tank, but the full rates of adjuvant for both
pesticides (basically a double dose of adjuvant for a given area). This is frequently the cause of
phytotoxic responses resulting from tank mixed applications. In the absence of supporting data, it is
inadvisable to lower the rate of either pesticide simply to avoid phytotoxicity
as it may impair the expected efficacy of the chemistry. The current hot and dry weather
conditions may exacerbate phytotoxicity.
Both Super Tin and Eminent fungicides have been linked to
potential yield loss in sugarbeet in recent field trials (see Boetel, Dregseth,
& Schroeder. 2003. Lygus Bug Control and Sugarbeet
Yield Impacts from
Timing – to ensure an economic return, the timing should be optimum for one or both pesticides. This is rare, consequently, one or both are being applied in less than optimum conditions (e.g. below or above threshold, inappropriate temperatures or crop stage, etc) and this may impair the efficacy of the chemistry and not obtain the desired result.
Jar test
Using appropriate safety equipment:
1) add proportionate amounts (convert gallons or pounds to ml’s, oz’s, or tsp’s) of components in clear quart jar (with liquid fertilizer carrier, many herbicide labels recommend two jars, 1 with, 1 without compatibility agents)
2) label jar(s) clearly, then fill one-half full with your carrier
3) add proportionate amounts of each of the products, one at a time, in the suggested order
4) gently shake or invert capped jar, let stand 15 - 30 minutes
5) if the mixture shows signs of physical incompatibility, shake the jar again to disperse ingredients
6) if it disperses, you will not need a compatibility agent but will need constant agitation in spray tank
7) if the mixture will not disperse after 2nd shaking, you may want to perform test again, with compatibility agent, or decide not to perform the tank mix
8) Recommended even if mixing has worked in different circumstances because of H2O differences
REMEMBER – this procedure
doesn’t check for chemical incompatibility
Two-Spotted Spider Mite Feeding Damage
– July 25, 2006
There’s been lots of info on the
e-mail lists and newsletters (see the links below) on two-spotted spider mite
biology, scouting etc but I thought I’d provide some images of spider
mite feeding damage – Click on the images for larger, higher resolution
images...
Two-spotted spider mites, adults, nymphs
and eggs
Early feeding damage (Stippling)
Damaged leaves
Damaged
fields (don’t let it get this bad!!)
Click here for
Jan Knodel’s e-mail piece on spider mites
Click here for Cropping Issues in the Northwest newsletter piece on spider mites
Soybean Aphid – July 19, 2006
REGIONAL UPDATE -
Soybean aphid populations persist in NW & WC MN and in
The pattern of local treatment is different this year with the first wide scale treatment starting up here in the upper/central Red River Valley, followed by the Fergus Falls area last week and apparently around the Morris area earlier this week. More areas of the state are reporting increasing populations so it appears this will be more of a state-wide problem than in the past couple of years.
THRESHOLDS - There has recently been a lot of discussion and questions on thresholds. The recommended threshold in both MN and ND, as in all but one soybean producing state, is 250 aphids/plant when aphids are present on most plants. Although lower thresholds have recently been reported, the 250 threshold was calculated using field data generated under production conditions in multiple locations in multiple states. It accurately reflects aphid population growth in commercial fields and does incorporate data generated under droughty conditions. A good description of the relationship between thresholds and aphid population dynamics was published by Dr. Phil Glogoza in NDSU’s Crop & Pest Report and is available at this website:
http://www.ag.ndsu.nodak.edu/aginfo/entomology/ndsucpr/Years/2004/May/20/ent_20may04.htm#SOYBEAN
Another description relating thresholds to plant stress (which used soybean aphids as an example) was written by Bruce Potter and can be found at:
http://swroc.coafes.umn.edu/SWMNPEST/05News/issue2/issue2.htm#ipm
TREATING LOW
POPULATIONS – Numerous trials conducted in
O’Neal,
M., and K. Johnson. 2005. Soybean aphids attack: Does
it pay to spray low populations?
Another trial conducted in
http://swroc.coafes.umn.edu/SWMNPEST/04publications/sbastjames.htm
SPIDER MITE REMINDER
- Keep an eye open for spider mites, they are favored by hot, dry weather. Look for spider mites first on the lower
leaves of the plant, the first damage will appear as small yellow spots
(stippling) and as feeding continues the leaves will turn yellow, brown or
bronze and drop from the plant.
While no threshold has been calculated,
Bottom Line
1) Continue to scout fields even if they’ve been sprayed.
2) The threshold of 250 aphids/plant is valid, calculated from production field data, and is the official threshold in all but one soybean producing state.
3) Treating low populations has been shown not to provide an economic return in numerous trials.
4) Keep an eye open for
Click
here for Dr. Ken Ostlie’s discussion of Soybean
Aphids, Drought and Heat.
Selected Past IPM Updates
July 05, 2005 –
Armyworm Flight, Crookston
June 06, 2005 –
Soybean Aphids – they’re back
May 23, 2005 –
Cutworms in Sugarbeets
July 2003 - Leafminer in Sugarbeets
May 2002 - Cutworms in Sugarbeets
July 2002 -
Armyworms in Small Grains
July 2002 -
Grasshoppers in The Red River Valley
Fall, 2001 - Soybean
Aphid in NW Minnesota
August, 2001 - Lygus in SugarbeetsJuly/Aug, 2000 - Armyworm Outbreak in RRV
Fall, 2000 - Soybean Aphid, A New Insect Pest in Minnesota Soybeans
June 20, 1999 - Potato Leafhopper, Grasshoppers, Cereal Insects
Sept 12, 1999 - Impact of Aster Yellows on Canola May be Greater Than You Think
Aug 31, 1998 - Lygus in Sugarbeets
Publications Available for Download
Insects
Grasshoppers -
Minnesota Grasshopper
Management - 2002 with color graphics
Minnesota Grasshopper
Management Brochure with scouting and control information (available as a
PDF file designed to be a tri-fold brochure).
Scouting -
Scouting for Insects
in Wheat, Alfalfa, and Soybeans - a manual prepared for the
Early Season
Scouting for Soybean Aphids - A guide to scouting early season soybeans for
soybean aphid.