Weed Control In Crops Research Articles

Pest and Weed Control in Crops, A Non-chemical Approach

Crops that are produced without manufactured fertilizers and protected from plant pests and weeds without manufactured chemicals are gaining in popularity among consumers. Non-chemical methods of plant protection, such as the development of biocides from plants, would be desirable for environmental and economic reasons and because of pesticide tolerance of some plant pathogens and insects. Extracts and their individual ingredients from several plant species have been used experimentally against plant pathogenic bacteria, insects, and weeds. There are problems, however, that make the use of biocides difficult: low concentration of active ingredients in the plants; purification of active ingredients from dozens of secondary compounds; instability of the active ingredients when exposed to light and air; and the mode of action is little understood or unknown. The technological and scientific advances that could allow the use of non-chemical based plant protection systems and the problems with such systems will be considered and discussed.

Vernal Seedling Emergence Model for Common Lambsquarters (Chenopodium album)

Knowledge of timing and extent of weed emergence before and immediately after crop seedbed preparation is needed to decrease need for preplant herbicides and increase efficacy of postemergence weed control in crops with either mechanical or chemical methods. Such knowledge is important for weeds that infest most crops over a wide area. For these reasons a mechanistic seedling emergence model based solely on soil temperature was developed for common lambsquarters. The model was validated using four sets of field data collected in 1988, 1990, and 1991 near Morris, MN. Agreement of predicted and observed emergence values across all site-years was 0.95 and the coefficient of determination (R2) was 0.98 (P < 0.001). Agreement for individual site-years was 0.96, 1.08, 1.08, and 0.98 and associated R2values were 0.99, 0.99, 0.99, and 0.98 (P < 0.001 for each site-year), indicating close agreement between predicted and actual emergence values.

Economics of improved spatial distribution of herbicide for weed control in crops

There are various causes of unintended spatial variability of herbicide dose in a crop, but each causes a reduction in profitability. The specific problem of spatial variability of the herbicide diclofop-methyl in postemergence control of ryegrass ( Lolium rigidum) is examined. A model of wheat yield response to herbicide application has been implemented in a microcomputer and used to analyse the economics of spatial variability. The economically optimal herbicide dose was found to be insensitive to spatial variability, but marked effects on profitability were observed. The costs of spatial variation of herbicide are estimated to be as high as 25% of net returns in some scenarios. For this case study, profit was found to be more sensitive to variance of herbicide dose within the path of the spray boom (due to nozzle design, wind, boom roll, etc.) than to variance due to overlap or underlap of the boom in successive circuits of the field.

Economic trade-off between pasture production and crop weed control

On wheat-sheep farms in the south-west of Western Australia, pasture production in winter is a major limiting factor for the sheep enterprise. This paper describes an economic evaluation of reducing herbicide usage in crops below recommended levels to increase subsequent pasture production in pasture-crop rotations. The analysis was of ryegrass ( Lolium rigidum) control by diclofop-methyl in the Merredin region and conducted using MIDAS, a whole-farm linear programming model. Inputs to MIDAS were provided by a simulation model of the weed population and regression models of weed kill from herbicide application and yield response to weed removal. Results indicated that the gains from increased sheep and wool production and reduced herbicide cost are likely to exceed the losses from reduced grain yield. This conclusion appears to be insensitive to major biological and economic assumptions of the analysis, although the issue of year-to-year seasonal variation has not been addressed.

RESPONSES TO RISK IN WEED CONTROL DECISIONS UNDER EXPECTED PROFIT MAXIMISATION

Risk is an important characteristic of decisions about weed control in crops. In this paper it is shown that risk can affect weed control decisions even if the objective of the decision maker is to maximise expected profits: that is, even if the decision maker is ‘risk‐neutral’ in the usual economic sense. This is shown for two decision frameworks: the optimal rate approach and the economic threshold approach. Empirical results are presented for control of ryegrass in wheat in Western Australia. It is found that, in general, risk reduces the optimal level of herbicide use under expected profit maximisation. Although individual sources of risk have a small impact on the optimal decision rules, combinations of uncertain variables can have a relatively large effect.

Herbicides in Peace and War

The herbicide industry, particularly that portion associated with the phenoxy herbicides, was given a tremendous boost by World War II but may have been mortally wounded by the war in Vietnam. Prior to World War II, there were very few herbicides and only a very tiny herbicide industry. Such things as common table salt, sodium nitrate, iron sulfate, and a few copper salts were tried for weed control in crops that were fairly resistant to those chemicals, and some people even tried using sulfuric acid. However, costs were high; killing weeds without injuring crops was not easy, and the chemicals were difficult to work with.

Herbicidal carbamates—benzenesulphonylcarbamates

A number of ring substituted alkyl benzenesulphonylcarbamates have been prepared and evaluated as selective herbicides. High activity associated with useful selectivity is obtained when the alkyl group is methyl and the benzene ring carries a 4-amino or 4-nitro group. The preferred compound is methyl 4-aminobenzenesulphonylcarbamate, common name asulam. All modifications of this structure resulted in compounds with less useful properties in respect of weed control in crops.

Penetration and Persistence of Diuron in Soil

The selective control of weeds in crops by the use of 3–(3,4–dichlorophenyl)–1,1–dimethylurea (diuron) has had considerable attention the last five years. Some of the problems of applying diuron are how long and at what depths the herbicide remains in the soil after treatment, with different methods and amounts of irrigation.

Uncommon Plant Growth Regulators for the Control of Nutgrass and Oxalis

THE recognition of the herbicidal activity in the phenylacetic T acids by Pybus et al. (2) is a matter of particular interest to those whose work is concerned with weed control in crops unusually sensitive to 2,4-D (2,4-dichlorophenoxyacetic acid) and its derivatives. Many crops will be injured by 2,4-D applications at the rates used in weed control, but are not particularly damaged by the use of 2,4-D in a spray directed at weeds, and from which only incidental amounts of 2,4-D come into contact with the foliage of the crop. However, there are some crops, e.g., cotton, which are severely damaged by 2,4-D at rates far below those in common herbicidal use. The pineapple plant is of about the same order of sensitivity to 2,4-D, but in a different way. Although pineapple may not be greatly injured by a chance application of 2,4-D in drift amounts (say 2 to 5 grams per acre) the crop may be forced to flower out of season, and the fruits produced on the immature plants are then too small to meet the standard can size. Although the formulation of the hormonal herbicide quite regularly spells the difference between success and failure in a commercial application, it has been our experience that an exceptionally wide range of 2,4-D and 2,4,5-T derivatives are ruled out of commercial use for weed control on pineapple plantations. Some 19 esters and other derivatives (alcohols, acetonitriles, acetamides, ethylsulfates, and the like) all have had more or less toxicty to nutgrass, but also have induced flowering in pineapples. Work by Wain (3), and his colleagues, has shown that there are a number of crops which are not adversely affected by chlorinated phenoxy-n-alkyl acids with an even number (more than two) of carbons in the side chain, although weeds common in the fields may be killed by these compounds. For some plants, the explanation for this apparently lies in the ability of the sensitive plants to convert 4-(2,4-dichlorophenoxy)butyric acid, for example, to 2,4-D, which is then toxic. Unfortunately, pineapple is forced to flower by 4-(2,4-dichlorophenoxy)butyric acid, although whether the compound is active in inducing flowering in its own right or only after beta-oxidation to 2,4-D may be debated. In any event, if growth regulators are to be used for weed control in the crop, some compound other than one containing the 2,4-D moiety must be used. Two weeds of increasing importance in pineapple fields under Hawaiian conditions are nutgrass, Cyperus rotundus, and a bulb-

WEEDKILLERS AS AN AID TO PASTURE AND CROP ESTABLISHMENT

Most agriculturists are familiar with the use of selective wcedkillers for the control of weeds in crops and newly sown pasture established in conjunction with conventional methods of cultivation. For cultivation mechanical aids are used to reduce interplant competition and to prepare a seed-bed. In this paper I propose to establish the concept of using weedkillers as a method of reducing inter-plant competition in place of mechanical aids. The concept is based on using one or two specific weedkilling chemicals to kill the existing vegetation in situ. Pasture mixtures are then sown into the dead turf or crops are drilled directly into the chemically destroyed turf. The paper is based on the work of the Extension Division of the Department of Agriculture.