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UC Pest Management Guidelines

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Common purslane, Portulaca oleracea.

Cucurbits

Herbicide Treatment Table

(Reviewed 12/09, updated 6/12)

In this Guideline: More about weeds in cucurbits:
Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
  Calculate impact of pesticide on air quality
Not all registered pesticides are listed. Always read the label of the product being used.
 
PREPLANT FUMIGATION
A. METAM SODIUM*
  (Vapam, Sectagon) 50–75 gal see label NA
  WSSA MODE OF ACTION GROUP NUMBER1: 27
  COMMENTS: Metam is a water soluble, soil-applied biocide. For best results, it should be applied to well tilled soil free of large clods that was moistened by rainfall or preirrigated 2 weeks previously in order to enhance germination of weed seeds. Typical application is with a subsurface spray blade into premade beds. Set spray blades to cut 2–3 inches below the soil surface with disc hillers following behind to form a 3- to 5-inch soil cap over treated area. After 7–14 days, the caps are removed and allowed to air before planting. Typically only a 6- to 12-inch band is treated in order to reduce costs. It can be injected into the sprinkler irrigation system and applied through drip irrigation tubes placed under a plastic mulch. There have been numerous failures with metam, mostly because of improper soil preparations. Fumigants such as metam sodium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
 
BEFORE PLANTING
A. BENSULIDE 5–6 lb a.i.    
  (Prefar 4E) 5–6 qt 12 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 8
  COMMENTS: A narrow-spectrum herbicide applied before weed seeds germinate; good for annual grasses and common purslane. Can be mechanically incorporated shallowly (1–2 inches) before planting, or applied after planting and incorporated with sprinkler irrigation. Can also be applied by chemigation, through sprinkler, surface drip, or subsurface drip irrigation. Very safe on all cucurbits. Also very persistent; check label for plantback (rotational crop) restrictions. Use allowed under a Special Local Needs label.
 
B. CARFENTRAZONE 0.00742–0.0296875 lb a.i.    
  (Shark) 0.5–2 oz 12 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: Rate depends on weed species. For best activity, apply when weeds are less than 4 inches tall or rosettes less than 3 inches wide. Provides control of emerged annual broadleaves, but has no preemergence activity. A nonionic surfactant or crop oil concentrate or methylated seed oil is required. Good spray coverage is essential for good control. Apply in a minimum of 10 gallons of water per acre.
 
C. GLYPHOSATE
  (Roundup Powermax, Touchdown, etc.) see label see comments NA
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  COMMENTS: A nonselective, foliar herbicide applied before planting to premade beds to kill emerged weeds. Restricted entry interval (R.E.I.) is 4 hours for Roundup and 12 hours for Touchdown. Allow 3 days after treatment before planting. Use the lower rate for annual grasses and weeds, the higher rate on perennial weeds. Add ammonium sulfate at 8 to 15 lbs per 100 gal to improve glyphosate activity if using hard water. Always add the ammonium sulfate to the water before adding glyphosate or other adjuvants. Add a nonionic surfactant for difficult-to-control weeds. Consult the label for specific recommendations on particular weed species. Do not apply to weeds stressed for moisture. For perennial weeds, allow 7 days after application before cultivating.
 
D. OXYFLUORFEN 0.25–0.5 lb a.i.    
  (Goal 2XL) 0.5–1 pt 24 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: Rate depends on weed size, but the rate used also determines the minimum period between treatment and planting: Cantaloupe = 60 days for the low rate and 90 days for the high rate; watermelon = 60 days for either rate; other cucurbits = 90 days for the low rate and 120 days for the high rate. Provides control of annual broadleaves both before and after they emerge. Incorporate with 2 inches of irrigation water and don't disturb soil until planting time. Work beds with a rolling cultivator or similar tool to a depth of 2.5 inches before planting to avoid crop injury or stand loss. Once beds have been worked before planting, the herbicide is no longer effective. However, crop injury can result if beds are not thoroughly worked before planting. This herbicide lasts 4–8 weeks in the soil and has a 10-month plantback restriction for nonlabeled crops. Apply in a minimum of 20 gallons of water per acre.
 
E. PARAQUAT* 0.5–1 lb a.i.    
  (Gramoxone Inteon) 2–4 pt 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: A nonselective foliar herbicide that kills emerged weeds. Can be used before planting or after planting but before the crop emerges. Any crop plants exposed to the spray will be killed, even germinating seed in the crook stage. No soil residual activity. Use the lower rate on small broadleaf weeds, the higher rate on larger weeds and grasses. A nonionic surfactant must be added at the rate of 8–32 oz/100 gal, with the higher surfactant rate needed for larger weeds and grasses. Wear protective clothing as paraquat is highly toxic if ingested, inhaled, or contacts the skin. Most active on warm, sunny days, particularly late afternoon.
 
AT PLANTING

Before crop and weeds emerge

A. BENSULIDE 4–6 lb a.i.    
  (Prefar 4E) 4–6 qt 12 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 8
  COMMENTS: A narrow spectrum herbicide, good for annual grasses and common purslane. Can be mechanically incorporated shallowly (1–2 inches) before planting, or applied after planting and incorporated with sprinkler irrigation. Very safe on all cucurbits. Also very persistent; check label for plantback (rotational crop) restrictions.
 
B. ETHALFLURALIN 1.12–1.6875 lb a.i.    
  (Curbit EC) 3–4.5 pt 24 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply to the soil surface within 2 days after planting and before crop and weeds emerge. In sprinkler-irrigated fields, activate with a minimum of 0.5 inches of water; a rainfall after application will also serve to activate it. Excessive irrigation or rainfall may move the herbicide deep in the soil, and injury can occur. In furrow- or drip-irrigated fields, a shallow cultivation will activate. Injury potential is greater if seeding depth is too shallow.
 
C. HALOSULFURON 0.023–0.047 lb a.i.    
  (Sandea) 0.5–1 oz 12 see label
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not use in watermelons. Controls many broadleaf weeds and suppresses nutdege.
 
AFTER PLANTING
After crop and weeds emerge
A. CLETHODIM 0.098–0.121 lb a.i. 24 14
  (Select Max) 13–16 fl oz    
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: Controls actively growing small grasses except for bromes and fescues. Apply to annual bluegrass at 4-leaf stage. Repeat treatments are necessary for perennial grasses, but a minimum of 14 days is required between applications. Do not apply a postemergence broadleaf herbicide within one day of clethodim or reduced grass control will occur. Symptoms appear in 7 to 14 days, depending on species and environmental conditions. Apply in 10 to 40 gal water/acre. Always add a crop oil concentrate at 1% v/v in the finished spray solution.
 
B. DCPA 4.5–10.5 lb a.i. 12 0
  (Dacthal 75W) 6–14 lb    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply at layby, when cucurbits have 4-5 true leaves, as a banded spray to control annual grasses and some annual broadleaf weeds. In sandy loam soils, maximum preemergence rate of 10 lb/acre is recommended.
 
C. HALOSULFURON 0.37–0.75 lb a.i.
0.5–1 oz 		12 30: pumpkins, cucumbers, squash
57: melons
  (Sandea)      
  WSSA MODE OF ACTION GROUP NUMBER1: 2
  COMMENTS: For use on seed and transplant cucurbits for the control of nutsedge. Apply over the top of direct-seeded cucumber, cantaloupe, honeydew, Crenshaw melons, pumpkins, and winter squash from the 4-true leaf stage through first bloom. Maximum use rates are lower for over-the-top applications (see label). Following bloom, or in other cucurbits including watermelon and summer squash, applications must be made either as a directed spray or with shields to minimize contact with the crop. Make applications to transplanted cucurbits at least 14 days after transporting but before 1st bloom. Following bloom, applications to transplanted cucurbits must be made either as a directed spray or with shields to minimize contact with the crop. Injury may result if the spray contacts the foliage. Use of 0.25 to 0.5% v/v of nonionic surfactant is recommended. Use of crop oil concentrate or silicone surfactants is not recommended because of increased risk of injury. Do not apply if a soil application of an organophosphate insecticide has been made. Do not apply a foliar organophosphate insecticide within 21 days before or 7 days after any halosulfuron treatment.
 
D. SETHOXYDIM 0.09375–0.28125 lb a.i.    
  (Poast 1.5EC) 0.5–1.5 pt 12 14
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: A selective, foliar herbicide for control of grasses. Addition of a surfactant (crop oil concentrate or nonionic surfactant) is essential. Usually safe to the crop, except on very warm, sunny days; this may be due to the surfactant. Injury observed has been small necrotic spots on treated leaves. Not effective on drought stressed grasses or on certain species (e.g., annual bluegrass, sprangletop).
 
LAYBY (Postthinning)
A. ETHALFLURALIN 1.12–1.6875 lb a.i. 24 0
  (Curbit EC) 3–4.5 pt    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply as a directed spray to avoid contact with the growing tips. Use when field is free of emerged weeds and incorporate with a sectioned rolling cultivator within 1–2 hours after application. Similar to trifluralin but also controls nightshades.
 
B. TRIFLURALIN 60: watermelon
30: all others
  (Treflan, etc.) Label rates 12  
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Rate is dependent on soil type. Apply as a directed spray to clean cultivated soil when the crop has 3–4 leaves. Immediate mechanical incorporation into the top 2–3 inches of soil is required. Leaves and runners contacted by trifluralin may be stunted temporarily; lobes on leaves may be thickened and veins constricted. Controls annual grasses and broadleaf weeds.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Group numbers are assigned by the Weed Science Society of America (WSSA) according to different modes of action. Although weeds may exhibit multiple resistance across many groups, mode of action numbers are useful in planning mixtures or rotations of herbicides with different modes of action. For more information, see http://www.hracglobal.com.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Weeds
W. T. Lanini, Plant Sciences/Weed Science, UC Davis
Acknowledgment for contributions to Weeds:
C. E. Bell, UC Cooperative Extension, San Diego County

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