Herbicides for Pre-Emergence Weed Control in Christmas Trees
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Dr. Jatinder S. Aulakh Valley Laboratory, Windsor, CT The Connecticut Agricultural Experiment Station 153 Cook Hill Road, P. O. Box 248 Windsor, CT 06095 Phone: (860) 683-4984 Fax: (860) 683-4987 Founded in 1875 Email: [email protected] Putting science to work for society Website: www.ct.gov/caes Herbicides for Pre-emergence Weed Control in Christmas Trees. Spring is almost here and it is time to plan What Weed Species Interfere with for pre-emergence herbicide application in Christmas Trees Growth? Christmas trees to control summer annual Many grassy and broadleaf weeds compete grassy and broadleaf weeds. For a pre- with Christmas trees for water, nutrients, emergence herbicide to be effective, it must light, and space. Most commonly be applied well ahead of weed seed encountered grassy weeds include: annual germination. However, before deciding on bluegrass, barnyardgrass, broomsedge, an herbicide, you must know your major crabgrass, goosegrass, fall panicum, foxtails, weed species. Therefore, regular scouting junglerice, quackgrass, and witchgrass etc. and correct weed identification are vital to The most common broadleaf weeds are: help select the most suitable pre-emergence annual sow thistle, Asiatic dayflower, herbicide for next growing season and get a chickweeds, common purslane, common bigger bang for your buck. ragweed, dandelion, field bindweed, field pennycress, goldenrod, hairy vetch, To increase the duration of weed control, horseweed, horsenettle, lambsquarters, consider a product with longer soil residual pigweeds, prickly lettuce, prostrate spurge, activity and use higher application rates, shepherd’s-purse, smooth bedstraw, smooth within label limits, depending on tree age, cat’s-ear, spotted spurge, wild carrot, and species, and soil type. The higher the willow weed. application rate, the longer it takes for an herbicide to dissipate below the minimum What Pre-emergence Herbicides are threshold level. Always keep in mind that a Available for Controlling Weeds in pre-emergence herbicide will require 1/2 to Christmas Trees? 1 inch of water from rainfall or irrigation for A fairly good number of pre-emergence activation. Therefore, either time your herbicides are available for broadleaf and application within a few days before rainfall grassy weed control in Christmas trees. or apply a light irrigation. Do not apply pre- However, factors such as Christmas tree emergence herbicides on snow or frozen soil species and age, weed species to be and also make sure the ground is free of controlled, environmental safety, and thatch or other debris which may intercept economics must be considered to select an the herbicide from reaching the soil. herbicide most suitable to your situation. Herbicides for Pre-emergence Weed Control in Christmas Trees, J. Aulakh The Connecticut Agricultural Experiment Station (www.ct.gov/caes) Herbicides commonly used for weed control 2. Root Inhibitors: This group consists of in Christmas trees belong to one of the Dinitroaniline herbicides such as following groups: Pendimethalin, Oryzalin, and Trifluralin etc. 1. Photosynthesis Inhibitors: This group Dinitroanilines are largely absorbed by consists of triazine herbicides such as young seedling shoot organs such as the Atrazine, Simazine, Prometryn, and hypocotyl or coleoptile and to some extent Hexazinone etc. Atrazine is mainly effective by plant root systems. They are very on broadleaf weeds. Simazine has both grass effective on grassy weeds as well as some and broadleaf activity. They are absorbed dicot weeds such as pigweeds and both by roots and foliage. They bind to a lambsquarters. Other dicots such as protein involved in electron transfer in ragweeds and smartweeds are not adequately Photosystem II, thereby inhibit controlled. Dinitroaniline herbicides act by photosynthesis which results in chlorosis of inhibiting cell division (mitosis) and kill plant leaves followed by necrosis of leaf susceptible plants by inhibiting cell division tissue and eventually death of the whole in root cells which arrests normal root plant. Triazines have excellent soil activity. growth. Their soil persistence varies from a few Weeds Controlled weeks to many months depending on Dinitroanilines control annual bluegrass, product, use rate and soil pH. Triazine- barnyardgrass, crabgrass, crowfootgrass, resistant weeds have been confirmed in foxtails (yellow, green, and giant), several states in the US following repeated goosegrass, itchgrass, Johnsongrass (from use of these herbicides. seed), junglerice, lovegrass, panicums Weeds Controlled (browntop, fall, and Texas), sandbur, Atrazine controls annual morningglory, signalgrass, sprangletops (Mexican and red), cocklebur, groundcherry, kochia, witchgrass, woolly cupgrass, carpetweed, Jimsonweed, lambsquarters, nightshade, common chickweed, mouse-ear chickweed, pigweed, ragweed, purslane, velvetleaf, wild cudweed, evening primrose, filaree, Florida oats, and witchgrass. pusley, henbit, horseweed, kochia, Simazine will control alyssum, annual lambsquarters, lawn burweed, London bluegrass, annual ryegrass, barnyardgrass, rocket, Pennsylvania smartweed, pigweed, crabgrass, downy brome, fall panicum, puncturevine, purslane, shepherdspurse, foxtails, goosegrass, junglerice, signalgrass, spurges (annual and prostrate), speedwell, silver hairgrass, wild oats, rattail fescue, velvetleaf, and yellow woodsorrrel. witchgrass, annual morningglory, Oryzalin is weak on annual morningglory, carpetweed, common chickweed, fiddleneck, climbing milkweed, ladysthumb, london filaree, fireweed, Florida pusley, groundsel, rocket, mustards (black and wild), henbit, knawel, lambsquarters, nightshade, nightshade (black), prickly lettuce, prickly pepperweed, pigweed, pineappleweed, sida, prostrate spurge, spotted spurge, prickly lettuce, common purslane, ragweed, ragweeds (common and giant), smartweed, redmaids, Russian thistle, shepherd’s-purse, sowthistle, and velvetleaf. smartweed, Spanish needles, speedwell, 3. Shoot Inhibitors: This group comprises of tansy mustard, and wild mustard. chloroacetamides herbicides such as Pennant Herbicides for Pre-emergence Weed Control in Christmas Trees, J. Aulakh The Connecticut Agricultural Experiment Station (www.ct.gov/caes) Magnum etc. Shoot inhibitor herbicides are Gallery 75 DF, Marengo, and Specticle. absorbed by germinating seedling shoots These herbicides affect cell wall prior to or at the time of emergence. They biosynthesis in susceptible weeds and block the formation of long chain fatty acids. prevent cell division in developing root tips. Pennant Magnum effectively controls many Seeds of treated plants germinate but they annual grasses, Asiatic dayflower, yellow either fail to emerge or emerge as severely nutsedge and black nightshade. Typical stunted seedlings. Gallery is mainly a persistence in the soil is 10 to 15 weeks. broadleaf herbicide and does not have Weeds Controlled activity on grassy weeds. It may be applied Pennant magnum controls annual bluegrass, over-the-top in established field grown barnyardgrass, crabgrass, crowfootgrass, conifer species listed on the Gallery 75 DF foxtails (yellow, green, and giant), label (consult product label). Marengo and goosegrass, Johnsongrass (from seed), Specticle are newly registered products junglerice, fall panicum (browntop, fall, and for use as fully directed sprays in field Texas), sandbur, witchgrass, carpetweed, established Christmas trees. However, common purslane, common groundsel, hairy there is very little experience with these galinsoga, nightshade (black and hairy), and herbicides in the Northeast. Over-the-top Florida pusley. Pennant magnum also application of Marengo/Specticle may controls annual sedge and yellow nutsedge. seriously injure Christmas trees. 4. Shoot and Root Inhibitors: This group Marengo/Specticle control annual grassy as comprises of herbicides such as Devrinol well as broadleaf weeds. These products do 50W or 5G (Napropamide). Devrinol is a not control plants emerging from tubers, long residual herbicide labeled for use in rhizomes, bulbs, corms, existing rootstocks, conifer seedbeds and transplant beds. It and woody vegetation. controls most annual grasses and many Weeds Controlled broadleaf weeds. It is weak on common Gallery 75 DF controls asters, bittercress, ragweed, yellow woodsorrel, spurge, carpetweed, chamber-bitter, chickweeds, nightshade, and horseweed. common groundsel, common ragweed, curly Weeds Controlled dock, dandelion, dogfennel, eclipta, Devrinol controls annual bluegrass, fleabanes, honeyvine milkweed, horseweed, barnyardgrass, barleys, bromes, canarygrass, henbit, Jimsonweed, lambsquarters, London crabgrass, foxtails, goosegrass, seedling rocket, mustards, nightshade (black), Johnsongrass, panicums, Italian ryegrass, pepperweed, pigweeds, plantains, prickly sandbur, sprangletops, stinkgrass, annual lettuce, red sorrel, shepherd’s-purse, spiny sowthistle, carpetweed, common chickweed, sow thistle, spurges, swinecress, tansy common groundsel, common lambsquarters, mustard, white clover, wild carrot, wild common purslane, horse purslane, little mustard, wild radish, willoweed, and wood mallow, prickly lettuce, prostrate knotweed, sorrels. pineappleweed, purple cudweed, redstem Marengo/Specticle labels indicate control of filaree, and redroot pigweed. annual bluegrass, crabgrass, foxtails, and 5. Cellulose Biosynthesis Inhibitors: This ryegrass and broadleaf weeds such as group comprises of herbicides such as bittercress, chickweeds, clover, cudweed, Herbicides for Pre-emergence