Managing Slugs with Baits & Acknowledging Other Pests in Grasses Grown for Seed
and Their Rotational Crops in No-till Willamette Valley
Prepared by: A.J. Dreves (CSS Dept.), G. Fisher (Emeritus CSS), & W. Gavin (retired USDA-ARS) 05/10/2016
Slugs and other pest insects are an increasing problem in Willamette Valley grass and legume seed crops. This draft document explores the problems and offers suggestions for controlling slugs with use of baits. No-till seeding systems and increased organic matter in Willamette Valley grass seed fields are developing a persistent group of pests causing increasingly greater economic losses in grass seed and rotational crop production. Slugs, crane flies, symphylans, cutworms, wireworms as well as stem and leaf feeders like frit fly, meadow spittle bug and plant bugs were buried or burned in the past. Cultivation can crush, bury, or otherwise kill significant numbers of pests. Field burning eliminated populations of the stem/leaf feeders above by destroying straw residues containing over-wintering eggs of the pests. Field burning reduced the amount of post harvest residue that provided food, habitat and moisture essential for increasing populations of certain pests like slugs. Even-rolling a seed bed at planting has helped prevent or delay some pests from getting to and damaging seeds and young seedlings. Slugs and symphylans must use existing tunnels, cracks and crevices to reach seeds. This delay can help establish that seedling stand.
Slugs and Control Timing
Populations of the gray field slug (GFS), Deroceras reticulatum in some Willamette Valley grass seed fields are exceedingly large. Fall and spring seedings will be at risk. In the absence of tillage, growers rely nearly exclusively on metaldehyde, iron phosphate, and chelated iron baits or liquid sprays to manage slugs. These products can be quite effective with proper timing, rates and the right weather conditions. However, be aware that biological and non-biological factors can affect level of control achieved from these products. WEATHER: There is a window of time in the fall until perhaps mid-NOV when slug activity and weather favor baiting for control. From mid-NOV through mid-MAR (approximate) control of slugs with all metaldehyde and iron phosphate products is less than satisfactory. This is most likely due to lower temperatures, increased and steady rain and windier conditions. Bad weather slows slug movement and visitation, so mortality from baits and liquids declines. As temperatures increase from Mid- MAR through MAY, a large window of opportunity may open for slug management. However at this time, weather conditions for optimum control and entry, into fields may be limited to brief periods. Also NIGHTCRAWLERS, particularly in no-till fields remove significant numbers of the bait pellets each night (up to 20%). Research is showing that metaldehyde granules and sprays can give better control of GFS than pelleted baits on spring seedings. On established seedings of perennial rye grass (PRG), this timing can protect tillers and even flag leaves from damage that may significantly affect yield.
Arion sp. feeding on grass blades.
Other Pests Contributing to Losses
Other insect and arthropod pests including black cutworm, wireworm, European crane fly, symphylans, billbugs, frit flies, pillbugs, and millipedes contribute to poor seedlings. Like slugs, these pests are causing increasingly greater losses each year to new seedings. Damage may be mistaken for that of slugs, so monitor for the signs and symptoms, properly identify the cause and treat accordingly with the appropriate treatment. When these insect problems have been diagnosed or expected based on previous season populations, Lorsban® is labeled on PRG and usually helps abate damage. It can be broadcast applied at 1 qt/A at seeding if soil moisture is sufficient for seed germination or shortly after rains to stimulate seed germination. Critical timing for frit fly control is to protect seedlings through the four to six leaf stages. Frit flies are active shortly after first consistent rains in SEPT or OCT. This treatment helps control all in both fall and spring-seeded fields but not the toughest soil pests—wireworms and symphylans. Wireworms and symphylans: If these 2 pests are present, an incorporation of Lorsban to soils with adequate moisture may provide suppression sufficient for the stand. However, Lorsban can affect predatory beetles.
Slug Control Suggestions
At Seeding Time and Establishing a Stand
Early Fall seedings, before significant slug movement and feeding above ground; and before too much rainfall and colder weather.
At Planting: Broadcast 10 to 15 lbs/A of weather-fast Metaldehyde bait. Even though few slugs may be active on soil surface at this time, most baits should retain molluscidal activity from application through the first episodes of fall rains. Bait again if necessary.
After Planting*: Broadcast 10 to 15 lbs/A of metaldehyde or iron phosphate bait or a combination of the two. Wait and apply when slug activity is noticed in the newly seeded field, whether grass has emerged or not. Inspect fields in early morning when dew present and slugs would be active.
*In either case, a second application is usually necessary, if bait is gone and slug damage or slug presence are still noticed. Make this second application before NOV 1, because when temperatures drop into the 40’s °F, and windy and rainy conditions prevail (early NOV, usually), bait visitation is reduced – so is control of slugs.
Late Fall seedings, after slug activity on soil surface has begun and damage is imminent at seeding; rain increases.*
At Pre-plant: Broadcast baits prior to seeding, when GFS is active and feeding on previous crop or weed residue. Broadcast 10-15 lbs/A of either iron phosphate or metaldehyde bait. --AT Pre-plant: Broadcast spray liquid metaldehyde (Slugfest®) from 1½ to 2 qt/A in the early AM if there are a lot of crop or weed plants that slugs are feeding on.
*Control of GFS should be completed prior to early NOV in most years. This is because cold temperatures, wind and rain can greatly impede control by reducing the total time that slugs spend above ground searching for food.
Slug Control when Spring Seeding
(mid-MAR to MAY)
Rain, cold temperatures and wind are common in the spring and inhibit slug activity and compromise control efforts. The GFS population at this time is often skewed to juvenile slugs. The young slugs prefer organic matter soil. They can be quite difficult to draw to baits and to control in general. Additionally, large populations of nightcrawlers on our no- till soils have been shown to remove up to 20% of pelleted slug baits in just the first night after application in late winter and spring months.
Control slugs in the previous crop and/or the previous fall. Don’t wait for the following spring to begin slug control at seeding time. Assess slug populations and apply controls during the summer and late fall of the preceding year when appropriate. (See above for Early and Late Fall Seedings) Even when controls have been applied the previous fall, spring seedings may still be at risk from slugs. This is particularly true for the grasses slower to germinate and those plantings that have seedling diapause in summer (Tall Fescue, Fine Fescue).
At Planting: In-Furrow or On-furrow application of metaldehyde bait with seed: such as Meta-rex shorts 5 to 7 lbs of bait/A.
Broadcast metaldehyde or iron phosphate bait, 10 to 15lbs/A**
At Planting: Durham G (3.5 or 7.5%) appropriate rate dribbled over seed row
Slugfest® at 1½ to 2qts/A sprayed at night if slugs are active.
Followed by: Broadcast metaldehyde or iron phosphate bait, 10 to 15lbs/A **
Durham G (3.5 or 7.5%) appropriate rate dribbled over seed row
Slugfest® at 1½ to 2qts/A sprayed at night if slugs are active.
** Control with pelleted baits whether iron phosphate or metaldehyde in late winter and spring may not be effective in some fields because of: 1) bait removal by earthworms, and 2) likelihood of persistent, poor weather conditions that inhibit slug feeding and promote bait degradation.
Slug Control in Established Seedling or
First Year Stands
(early-MAR, mid-APR, Early MAY)
Consider spring slug control in fall seeded grasses older stands to reduce crown damage and promote tiller development. These are critical times in seedling and tiller development.
Some baits have performed well under cold, wet conditions. However, earthworms are still a potential factor in bait removal. So, if sufficient foliage is present, consider Slugfest® foliar spray applied on an evening when slugs are active and weather will be conducive for extended slug activity. Durham G may also be an option over the row. A second application at the end of this period may be necessary.
|Slug Control in Established Perennial Ryegrass|
Perennial Ryegrass (PRG) has by far the largest populations of slugs to infest various grasses grown for seed. Significant damage can occur, even after the establishment year. Consider that in the fall, late SEPT and OCT, many of the slugs are mature. Controlling these slugs prior to egg deposition is essential to population control and damage reduction. Fall weather can sometimes provide a window of opportunity for control.
10 to 15 pounds of metaldehyde or iron phosphate bait is recommended as a broadcast application to PRG after soil moisture has increased and temperatures have dropped sufficiently for sustained above ground activity. This may have to be repeated when slug populations are large.
1½ qts Slugfest with the above timing. Apply at night when slugs are on foliage. It should be applied when no rain is expected for the next few days and nights are calm and warm- conducive to slug activity. DO NOT APPLY in rain or when slugs are not on foliage.
Durham G (3.5 or 7.5%) appropriate rate dribbled over seed row. Always verify suggested uses and rates are legal. Have current label in possession. Be sure that damage and/or seedling loss is in fact due to slugs and not other pests or a combination of pests such as Black cutworm, garden symphylan, wireworms, cranefly larvae, billbugs, and fruit flies.
Summer Control in Previous Crop (White Clover)
(JUNE and JULY)
GFS feeds at night on clover foliage in JUNE and JULY, whenever sufficient moisture occurs on leaves. This happens after a rain or for a few hours in early AM when dew is present. The dew point is often surpassed in the micro-climate of clover canopy for a few hours in the early AM.
Broadcast spray liquid metaldehyde (Slugfest®) from 1½ to 2 qts/A in early AM when slugs are on foliage. Do not apply to bloom if bees present.
Broadcast iron phosphate bait, (Sluggo®) 10 to 15 lbs/A, in JUNE or JULY. (Sluggo® can be applied anytime of day).