Timing is everything when it comes to killing weeds. You can have the right product and tools, but if you apply the weed killer at the wrong time it can have a diminished effect or no effect at all. For instance, excessively cold or hot weather can hinder the effectiveness of weed killer. If you want to see results, follow these simple guides when you spray for weeds in your lawn.
Once you have chosen the correct weed killer for your lawn and decided how to use your weed killer, the good news is you should begin to see results soon.
Some herbicides work extremely quickly, even causing weeds to wilt within a few hours after application. In contrast, some special formulations designed to control specific weeds may require a bit more patience. Once standard Roundup has been sprayed on weeds, you will often see results within 2—6 hours. These may not show results for up to 12 hours.
If you want to kill broadleaf weeds in your grass, you will usually end up using a selective weed killer designed to kill broadleaf weeds, or you may choose one of the best weed and feed products on the market. Weed and feed formulas often combine broadleaf herbicide with grass fertilizer, to get rid of weeds and improve grass health.
After applying your weed control solution, you will typically begin to see weeds begin to die within 5—7 days. Most weeds should be completely eliminated 2—4 weeks after application. Fast results, but you have to be careful. Glyphosate is a non-selective herbicide that will kill any plant it is applied to. Different products work best to kill different grasses. Pre-emergent weed killers work quickly. However, because they kill seeds just as they begin to sprout, this process is often invisible.
When late spring rolls around and you see no new tufts of crabgrass or sprouting chickweed, the pre-emergent weed killer has done its job. If you do see annual weeds returning to your lawn, this may be because the pre-emergent weed killer was applied too late or washed away by excessive rain. They usually are applied to the foliage, but are also effective in the soil. Any herbicide that falls on the soil instead of the foliage can be percolated into the soil with rain or irrigation and will be taken up by weed roots.
Phenoxy growth regulator herbicides have the least plant activity and soil residual activity; the carboxylic acids generally have the most. Broadleaf crops and turf grasses should not be planted into soils recently treated with these herbicides because they severely inhibit seedling emergence.
The most common symptoms for these herbicides are leaf and stem malformations. In cotton plants, points develop on leaf edges. Overapplication or application at the wrong stage of development in corn can cause leaf rolling and crinkling, brace root malformation, sterile flowers, and missing grain blasting.
Blasting and malformed seed heads are common symptoms of ill-timed applications in wheat. Vapor from these products can easily drift to desirable plants, so they must be applied carefully. Equipment should be cleaned according to label instructions before it is used to treat susceptible crops with other herbicides.
Herbicides in this category inhibit photosynthesis, the process by which all green plants convert light energy from the sun into sugars food. Photosynthesis inhibitors are broadleaf herbicides, but also control annual grasses to some extent. Their selectivity when applied postemergence depends on the crop and application method.
Herbicides in the triazine, triazone, uracil, and urea families move within the plant and exhibit these symptoms in older leaves first: yellowing between the leaf veins or in the veins, and yellowing of the leaf margins that eventually turn brown and die.
Herbicides in the benzothiadiazole, nitrile, phenyl-pyridazine, and amide families are not mobile within the plant and affect only treated leaves. Symptoms include speckling, spotting, and yellowing or bronzing that may kill affected tissue. Soil pH higher than 7. Herbicides classified as pigment inhibitors destroy the green pigment chlorophyll in leaf tissue.
Chlorophyll is necessary for photosynthesis; without it, plants die. These herbicides are absorbed by roots and translocate to the shoot tissue where they inhibit the production of carotenoids—substances that protect the chlorophyll molecules that make plants green.
Without carotenoids, chlorophyll is destroyed. These herbicides do not destroy carotenoids already formed, but prevent the formation of new ones. There are three families of herbicides that bleach plant tissue. Injured leaves turn yellow or white, then often translucent. New growth is yellow to white with sometimes a hint of purple or pink.
These symptoms can be found on cotyledons to the newest leaves of susceptible plants. If the insecticide is placed incorrectly or applied at the wrong rate, cotton may be injured. Consult the label for further precautions. Some herbicides act on seedling weeds shortly after they germinate and before they emerge.
These herbicides work beneath the soil so their effects are seldom seen. If overapplied, however, they may inhibit growth of weed or crop seedlings that do emerge through the soil surface.
These herbicides can be divided into two groups—root inhibitors and shoot inhibitors. Root inhibitors. These herbicides interrupt cell division, which stops root growth in seedling weeds. Plants die because they cannot take up enough water and nutrients to sustain growth. The root inhibitors are most effective on small-seeded broadleaf and grass weeds.
Large-seeded weeds and crops generally survive normal dosages because their roots and shoots grow through the herbicide treated zone in the soil. Shoot inhibitors. The seedling shoot growth inhibitors also act on newly germinated weed seeds. They are absorbed by the seedling shoots of grasses and roots of broadleaf plants, and they disrupt cell growth.
They are most effective at controlling small-seeded grass and broadleaf weeds. Large-seeded crops and weeds are not usually affected. Once tolerant or susceptible plants emerge they can generally overcome the effects of the herbicide.
Injury to tolerant plants is caused by root damage. Grass crops may be stunted and have a purple discoloration because roots cannot take up enough phosphorus. Root systems appear stubby and thick, especially the lateral roots. Broadleaf plants may have swollen and cracked hypocotyls.
If these herbicides are incorporated shallowly or applied preemergence, they sometimes cause callus tissue tumors to form on the plant stem at the soil surface.
This weakens the stem and causes lodging. Dinitroaniline herbicides applied postemergence to broadleaf crops may cause stunting. Symptoms caused by the shoot inhibitors are much different than those of the root inhibitors. Overapplication or extended periods of cool, wet weather shortly after planting may sometimes cause injury to tolerant crops such as corn or sorghum. In broadleaf plants, the center vein midrib may draw in the leaf edge in a drawstring effect.
Leaf puckering is also a symptom on broadleaf plants. There may also be stunting that persists until the soil warms enough to promote plant growth. These products are widely used in Texas row crops, turfgrass, and horticultural crops.
The growth inhibitor herbicides have no postemergence activity; therefore, the timing of application is critical. Dinitroanilines have various requirements for incorporation into the soil.
Consult the individual product label for specific recommendations. The cell membrane disruptor postemergence herbicides control both grasses and broadleaf weeds by destroying cell membranes and causing rapid desiccation of the plant. There are two types of cell membrane disruptor herbicides: the bipyridylium and the diphenylethers. Although glyphosate that has spilled or over sprayed into soil breaks down in the soil, it takes some time. Approximately half of the herbicide degrades within two and days, largely dependent on soil moisture and climate.
Studies in earthworms, rats, mice and rabbits revealed that their rate of growth and the incidence of cancer were affected when fed high doses of glyphosate over a period of 18 and 24 months, so the time glyphosate needs to work as a toxin on mammals often is longer than its presence in soil might allow. Glyphosate is miscible in water, meaning that it remains viable — and toxic not only to plants, but also to certain aquatic species, says the National Pesticide Information Center.
Glyphosate herbicides contain surfactants, such as polyoxyethylene amine POEA , that can be as dangerous as the acids and salts in the compound. The herbicide works on aquatic life in large concentrations, such as occur when unused product is dumped in a storm sewer.
0コメント