Spray tank cleanout | Drift control | Cutworms
Wind and rain have delayed weed control. We have articles this week on how to reduce spray drift when spraying in a little wind, and how to clean the tank properly between fields. Without a proper cleaning, unwanted damage can occur from residues accumulating in the tank and sprayer plumbing — especially if the sprayer is sitting full and ready to go.
The same rains that have delayed spraying can also increase nitrogen and sulphur leaching in lighter soils, and increase denitrification in heavy soils. While very good soil moisture conditions may increase canola yield potential, those rains may have depleted the nitrogen reserves somewhat. Top dressing is an option to restore those reserves and maintain yield potential.
The insect watch this week includes cutworms, diamondback moth and flea beetles, and when scouting keep your eyes open for wireworm, early season blackleg lesions (especially in tight rotations) and anything else unusual. With moisture stress, yellowing and damping off may show up due to environmental stress, rhizoctonia (wirestem) and other opportunistic root pathogens.
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Some herbicides left in the tank for an extended period can lose a large amount of their herbicide activity. Some may also leave deposits that if not cleaned out well, may come back into the spray solution in subsequent sprays. This can be costly to sensitive crops.
And finally, common canola-crop herbicides and surfactants left in a tank for any extended period of time can remove herbicide residues from tank walls and sprayer plumbing. Some of these loosened residues can be very damaging — even lethal — to a canola crop.
If wind or rain delays spraying, the concentration of scrubbed-free herbicides in the tank can continue to increase.
This underlines the importance of a complete clean out between products, and of an understanding of what risks each product and each tank mix presents in terms of scrubbing effect and what may happen to a product or products if left in the tank for an extended period.
The following tips will help prevent this from happening:
Spray immediately after filling and spray until the tank is empty. It’s OK to cover previously sprayed areas – all herbicides must be crop-safe at twice the label rate to be registered by the PMRA. Reduce the rate to be certain. Second, add 10x the sump’s remnant of clean water, circulate, and spray it out in the field as well. Repeat.
Look for solid herbicide residue. Some herbicides may precipitate out of solution and many dry herbicides use clay as a carrier. These particles can become trapped in some parts of the sprayer or plumbing. Visual inspection can identify these problem areas and ensure that they are cleaned properly.
Apply direct pressurized spray to all parts of the tank wall.
Empty the sump as completely as possible by spraying it out. The only way to remove the remaining herbicide is through dilution by repeatedly adding water and each time draining the sump as much as possible.
Pump clean water through the boom. Check that all return and agitation lines also receive clean water. Flush all residue. This may require opening and closing various valves several times, and repeating the process with new batches of clean water.
Many small washes better than one big one. For example, a single 600 gal wash is as effective as two washes with 70 gallons each, and three with 30 gal each, assuming a 10 gallon sump remainder.
Filters. Nozzle screens and in-line filters can be a significant reservoir for undiluted or undissolved herbicide and are one of the most overlooked parts of sprayer decontamination. Remove all filters and nozzle screens and thoroughly clean these with fresh water. Run clean water through plumbing leading to the screens.
Nozzle bodies. When rinsing the boom, rotate through all nozzles in a multiple body. Remove screens that may have been used with herbicide, even if just for a short while.
Tank cleaning additives. Good tank cleaning has 3 key elements:
1. Ammonia has some ability to break down oils or “degrease” but its main affect is to raise the pH of the cleaning solution, which helps increase the solubility of sulfonylurea (SU) herbicides. This allows more of the SU residue to dissolve in the cleaning water and be flushed from the tank.
2. Detergent. When decontaminating after use of an oily (EC) formulation or oil-surfactant blend or solvent-based adjuvant, a strong detergent will break down oily films that may trap other herbicides such as SUs on tank and hose material.
3. Surfactants reduce the surface tension in water so that as much water drains from the surfaces of the sprayer as possible. Another use of surfactants is in “spot-free rinses” at car washes. The surfactant allows the dirty water to run off the car and prevent spots. In your sprayer, spots could contain herbicide residue.
There are several all-in-one tank cleaners on the market that contain elements of all three components in one product for convenience and ease of use. Check with comprehensive tank cleaner manufactures to ensure that they have all of the components that you require
Rinsate disposal. Always spray out the tank in the field. Do not drain the tank while stationary unless you are certain it is free of pesticide and that you are away from sensitive areas and waterways. Another option is to build a biobed for rinsate disposal near the yard. A biobed is a clay-lined hole filled with a mixture of topsoil, peat or compost, and straw. This rich microbial environment can speed the breakdown of pesticides. Biobeds are a new concept in Canada but are considered a best management practice in Europe. Research continues to see how well they work in Canadian moisture and temperature conditions. Click here for an article about an AAFC study.
Rain and wind have delayed spray operations, leaving some very short windows to get important herbicide spraying done. Here are some drift management tips that can work in combination to help reduce the risk of drift and perhaps make those short spray windows just a little bit longer.
1. Do not spray in winds above 15 km/h (9 mph)
2. Do not spray in dead calm conditions in early morning, night or late evening. In dead calm, temperature inversions can cause fine droplets in spray to hang in the air and settle anywhere — and often not where you want them. Ground fog or dust that seems to hang in the air is a good indicator of these inversion conditions.
3. Slower ground speeds will help keep pressures down. When you increase travel speed, spray pressure must increase considerably more to maintain the spray rate per acre. For example, if you increase speed by 10%, pressure may have to increase by 25%. With conventional nozzles under higher pressure, droplet size shrinks and drift potential increases. Know what speed range your nozzle provides to achieve coarse sprays. This range may be fairly narrow for high pressure nozzles. For low pressure nozzles, the speed range tends to be a lot wider.
4. Choose a nozzle that produces a coarse spray in the middle of its pressure range. A nozzle that produces a coarse spray through the middle of its pressure range gives you the most flexibility to change spray pattern and droplet size as you adjust ground speed and pressure. For example, if you have a nozzle that produces coarse spray at 40 to 80 psi and you’re working at 60 psi, this nozzle gives you the flexibility to slow down or speed up and still achieve a coarse spray. Many low-drift nozzles are now priced competitively with conventional extended range nozzles. (See the tables at the bottom of this article.)
5. Operate nozzles at their minimum recommended height. A boom at 50-60 cm (20-24”) above the target will have half the drift of a boom 90-100 cm (36-40”) above the target. Auto-boom height controllers make it possible to lower the boom and maintain the desired travel speed without having to worry about the boom tips hitting the ground.
6. Avoid the combination of extra coarse droplet size and low water volumes. Extra coarse droplets and low water volume will not provide sufficient droplets per square inch to hit every weed with an adequate dose for good control.
7. Use a minimum of 45 L /acre of water unless otherwise specified for the product. Higher water volumes also help reduce drift since flow ratings (or orifice size) on nozzles have to be greater for a given speed, or speed has to be less for a given nozzle, either of which will reduce the number of fines produced by the sprayer.
8. Ensure that air flow from air assisted sprayers is properly set to minimize airblast rebound and drift.
Low drift nozzles, such as venturi nozzles, are better for some products than others.
9. Sprayer shrouds can reduce drift from 35% to 75%. As a result, buffer zone restrictions (set back distances from sprayed areas to sensitive areas or water bodies) are reduced on many product labels when shrouds are used.
These tips are from Tom Wolf’s “Spraying tips” webinar, the Guide to Crop Protection “Avoiding Spray Drift” article, and from Clark Brenzil, provincial weed control specialist with the Saskatchewan Ministry of Agriculture.
SMA has articles on Choosing the right spray nozzles.
For more on drift, click hereto read a Saskatchewan Ministry of Agriculture article called “Spray Drift — Causes and Solutions.”
Rain has set back weed spraying. Early canola crops are near the end of their spray windows, even though some fields have not received a first pass and some fields got a first pass but need a second.
Label application windows:
Glyphosate: Anytime up to and including the 6-leaf stage of canola.
Liberty: Cotyledon stage up to the early bolting stage of canola.
Odyssey/Absolute: 2- to 6-leaf stage of canola.
Herbicides applied after the approved crop stage could cause early flowers to be aborted. Click here to learn how. Growers are advised to assess what will create the greater losses — weed competition or loss of the first set of flowers? Canola typically produces more flowers than it can support. The plant can produce more flowers to compensate for early flowers that were lost, provided stress later in the flowering period does not limit this ability.
Aerial application may be required to spray within the application window if fields are too wet for the ground rig. Avoiding ruts is an additional benefit. Click here for aerial spraying tips. Note that Centurion has received emergency registration for aerial application on canola for 2012. For more information, click your province for a link to your guide to crop protection: Alberta Saskatchewan Manitoba
Minimize ruts with ground rigs. If you plan to use the field sprayer, wider tires and lower tire pressures can improve sprayer flotation and reduce rut depth. If the operator doesn’t have time to switch tires, make ruts parallel with the intended direction of travel for the swather and combine so growers can keep up their harvest speed.
Heavy rains can increase nitrogen and sulphur leaching in lighter soils, and increase denitrification in heavier soils. While very good soil moisture conditions may increase canola yield potential, those rains may have depleted the nitrogen reserves somewhat. Top dressing is an option.
Whether top dressing makes financial sense may depend on the conditions of the crop and how much nitrogen was available at the start of the season. If plants are strong and the crop looks good, this crop may provide the best return on investment from a top dress. Before applying, check what rates were applied at seeding or before. If rates were more than adequate for a high-yielding crop, some nitrogen could be lost to leaching or denitrification and not hurt yield potential too much. The healthy crop may also access leached nitrogen lower in the soil profile later in the season. But if rates were reduced in response to rising costs or lower yield outlooks at seeding time, this crop might benefit more from a top dress — especially if it looks in good shape right now.
How much nitrogen could be lost to denitrification and leaching? Growers can expect to see some nitrogen loss from extended heavy rains, probably in the range of 20-50%. Worst areas of the field — the low spots — could lose more of the available nitrogen. However, these saturated areas will have thinned crop anyway, meaning there may still be enough N to feed the few plants that remain.
Top dress products:
Urea: Top dressing urea with Agrotain provides a longer window to wait for rain to move the N into the soil profile where it is safe from volatilization, limiting losses while urea sits on the soil surface. If you know at least a quarter inch of rain is coming within the day, Agrotain won’t be necessary. If rain doesn’t come for a day or so, up to 5% of the urea could be converted to ammonia then nitrate and lost. However, more will be lost if rain doesn’t come for days and days.
UAN: A dribble band of liquid urea ammonium nitrate (UAN) works well.
Ammonium sulphate is a good way to apply N and S if you need both. It provides a wide window of application, with little potential for volatilization loss unless soil is alkaline.
Rather than trying to guess how much was lost, which will depend on rainfall, soil type, residue levels, organic matter — all of which make predicting loss very difficult — watch fields for visible signs of nitrogen deficiency and sulphur deficiency.
Nitrogen deficiencies look like (see photos at bottom):
—Leaves at the bottom of the plant are yellowing prematurely.
—No substantial biomass. Plants are thin and pathetic.
Sulphur deficiencies look like (see photos at bottom):
—Top leaves are small and narrow, and are often cupped.
—Short pods with little or no seed set.
—Pale yellow leaves
—Prolonged flowering if the crop is having trouble setting seed.
—Patchy look to the field. Sulphur is highly variable across a field, so deficiencies will usually show up in patches.
—Sulphur deficiency is more typical in sandy soil with low organic matter.
The ideal time for a nitrogen top up is before the 5-leaf stage, but top ups can be effective if applied after that time. Chances are soil nitrogen levels are enough to carry a crop through the first few weeks of peak growth, which starts after the 5-leaf stage. The top up will provide the nitrogen necessary to carry the crop through to full yield potential later when original reserves are drawn down. Sulphur can be top dressed anytime through to early flowering, but applications after first flower may not rescue full yield potential in deficient situations.
Click here for more tips.
Cutworms can leave canola fields with bare patches, clipped plants and large chunks out of stems and leaves. Flocks of birds — crows, gulls, etc. — can be a sign that cutworms are present in large numbers, but nothing beats digging to confirm your suspicions.
Cutworm thresholds are based on stand reduction, not actual cutworm counts. The threshold for canola is 25% to 30% stand reduction. With a stand reduction of less than 25%, canola plants may be able to branch out and compensate for some of the damaged or killed plants. However, if bare patches are developing as a result of cutworm feeding, these should be managed to limit their size, as the complete lack of plants does not allow for any compensation to occur. Spot spraying the patches and the surrounding crop where cutworms are present may be sufficient.
Here’s how to scout:
Start with an above-ground scout of the canola stand. Look for bare patches, holes or notches in foliage, and clipped plants.
Start digging where you find damaged or missing plants. Digging is required not to count the cutworms, but to confirm that cutworms are in fact present and feeding. Cutworms feed above ground at night and go below ground during the day. In moist soils, cutworms will stay close to the surface. In dry soils, they may go down 8-10 cm (up to 4”). Dig up soil from a one square foot area to a depth of 10 cm and put it into a basin. Loosen the soil and shake it up to activate cutworms. Also look for frass (cutworm excrement) around roots. Repeat a few times throughout the field.
Try to identify the cutworm species. Knowing the species can be helpful in fine-tuning the control measures.
Look for orange pupae. Cutworms are not feeding at this stage and are no longer a threat to this year’s crop. If most cutworms are greater than 1 inch, they will quit feeding and pupate soon, so an insecticide is less likely to provide an economical yield increase.
Look for wireworms. Wireworms are another below-ground feeder and can cause similar bald patches to appear in canola fields. All cutworms will curl into a ball. Wireworms do not. Wireworms are straw-colored and do not have a prominent head. No products are registered (or effective) for wireworm control in canola. If wireworms are the culprit, put away the sprayer and make note of areas or fields where the damage was higher. Remember these areas when planning crops and seed treatments for next year.
Cutworms surface at night to do their above ground feeding, so spray as close to nightfall as possible. Since not all cutworms will surface on a single night, it may take several days before full effect of the insecticide is achieved.
Cutworms do not feed during molting stages — when they shed and grow a new larger skin. This can take up to a week, and 20% to 50% of cutworms can be molting at any given time. Registered insecticides generally have long enough residues to be active when molting cutworms start feeding again.
Use high water volumes to get good plant coverage. Cutworms need to ingest the insecticide so the more surface area covered, the more likely that cutworms will take in the insecticide.
Cutworm damage will often appear in patches. If stand reduction is concentrated in small areas, a targeted application of a sprayer width or two around that area can be a lower cost and effective way to manage the pest compared to spraying a whole field.
Listen to CCC agronomy specialist Troy Prosofsky provide an insect update.
Add diamondback moth larvae to your early season scouting list. Canola fields in spots all across the southern Prairie are reaching thresholds where spraying may be required. This is much earlier than usual, and heavy feeding on cotyledon to 2-leaf plants may set back maturity — which is already on the late side. Growers cannot expect insecticide seed treatment to protect canola from diamondback moth larvae.
Before spraying, make sure that:
1. Large areas within the field have reached the nominal threshold of 25% or more of the leaf area lost. (See photos below.)
2. Diamondback larvae are still present.
3. They are actively feeding. (Many diamondback moth larvae may have started to cocoon (pupate) and are no longer a threat.)
4. Newest leaves are being eaten. If the newest leaves are in good shape, the crop will probably grow through the threat.
If you answer “yes” to all four, then consider a spray. If you answer “no” to any one, keep scouting. Situations can change — for the good or bad — in a matter of one or 2 days.
Feeding looks like: Leaves are chewed at the outside margins or in the middle, often leaving large areas missing. First instars will mine inside the leaf, leaving white tunnels. Later instars will also feed from the underside of leaves, leaving the top waxy layer — which will look like a window.
Flea beetles and diamondback larvae: Defoliation is defoliation — whether by diamondback moth larvae or flea beetles or both. The same four rules above apply to flea beetles. Only two products have both flea beetles and diamondback moth on the label — Lambda-cyhalothrin (Matador/Silencer) and Decis. If your target is only one of these insects, you will have other options.
Control may be reduced if applied above 25 C. Spraying later in the day as temperatures are declining is often better than earlier as temperatures are increasing.
If the immediate threat has subsided and most larvae seem to be cocooning, hold off on a spray. Parasitism by beneficial insects may take care of a large percentage of the population. A stretch of heavy rain may also curtail the next generation by washing feeding larvae off into ponded water or by increasing insect disease.
Watch Scott Meers talk about beneficial insects.
Moist conditions, good stands and tight canola rotations are contributing to blackleg and wirestem (rhizoctonia) in some canola fields. You can’t do much about wirestem at this stage, other than take extra care to protect a thinned stand from insects and disease throughout the year.
With blackleg, you do have control options.
Early blackleg infection — from the cotyledon to 3-4 leaf stages — leads to the greatest yield loss. If growers see blackleg lesions on cotyledons or leaves early in the season, this may indicate a greater risk of potential blackleg problems.
These tiny lesions may be tricky to spot, and you probably won’t see many of them. When scouting, also look for blackleg pseudothecia (black spots) on old canola residue, which may still be present on fields with a tight rotation.
Even if you can’t spot lesions on new plants or old stubble, the field could be at risk of serious blackleg infection.
Here are factors that increase the blackleg risk:
—Tight canola rotation
—Using the same variety many times in the rotation
—Yield loss to blackleg in previous years
—Using untreated non-certified seed
—Poor brassica weed control in previous years. These weeds can host blackleg in non-canola years
—Moist soils and warm humid conditions
If the above factors and your crop scouting suggest high risk for blackleg, consider fungicide as an additional tool to limit infection and yield loss. Headline, Propiconazole (Bumper, Pivot, Propel, Tilt) and Quadris are registered for blackleg management in canola. For more information on these products, click your province for a link to your guide: Alberta Saskatchewan Manitoba. If unsure about the decision, leave a few check strips and compare yields of treated to untreated areas.
Click here for more blackleg management tips.
June 14: Controlled Traffic Farming Crop Walk with Robert Ruwoldt, in Rolling Hills.
June 19: Canola, winter wheat and pulse crop tour, Lacombe
June 20: Growing with Canola crop walk, Hanna
June 20: Growing with Canola crop walk, Consort
June 21: Farming Smarter crop walk, Lethbridge
July 11-24: Public Crop Research Field Days
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