Weed competition

Estimated Crop Losses from Weed Competition... 

The total monetary loss resulting from weed competition in the cereal crops was 1.3 billion annually. The most frequently reported weeds were mustards (Brassica spp.) followed by wild oats (Avena fatua L.), bromes (Bromus spp.), and wild garlic (Allium vineale L.) (11). Losses in vegetables was 5% of the total while in fruit and nuts the loss was 7% of the total. Crabgrass, bermudagrass [Cynodon dactylon (L. )... 

Table I. Estimated average annual losses due to weed competition in crops, United States, 1975-1979...

In summary, weed competition with crop plants and their control constitute some of the highest costs in the production of food, feed, and fiber. In the United States, losses caused by weeds and the cost of their control totals about 15.2 billion annually. Total losses from weed competition with major crops produced in the United States is approximately 8.9 billion. 

Weed competition for water and nutrients can have similar effects on fruit quality as described above for fertilisation. For example, if weed competition is completely prevented by chemosynthetic herbicides in conventional production, this can lead to excess supply of certain mineral nutrients, in particular nitrogen and potassium, which in turn results in reduced sensory quality and shelf-life (Section 16.2.2). On the other hand, excessive weed competition, in particular, during the pre-bloom phase and the end of the first shoot growth period (Gut and Weibel, 2005), can induce nutrient and/or water deficiency and a risk of quality loss. 

Weibel, F.P., Ladner, J., Monney, P. and Sutter, F. (2006a). Improved organic and low-input apple production by weed competition tolerant rootstocks , Acta Horticulturae (.ISHS), Submitted Sept. 2006. 

Intercropping may facilitate weed control if intercrops are more weed competitive than sole crops or are able to suppress weed growth through allelopathy (the weed species is more susceptible to such phytotoxin than crops). If intercrops do not suppress weeds more than sole crops, they should provide yield advantages due to better utilization of resources or by converting resources than in case of sole crops (Liebman and Dyck 1993). 

Escape Shorter crop growth period and/or early ripening to be able to avoid the critical infestation period, or to have enough yield before the infestation becomes too severe (potato/late blight onion/downy mildew carrot/carrot fly) One or more monofactorial and multifactorial, durable resistance traits against pest and disease affecting yield and/or quality (scab/apple, late blight/potato, lettuce/downy mildew, yellow and brown leaf rust/wheat) weed competition by an allelochemical ability... 

Citrus trees are a long-term investment, and growers cannot afford crop damage or yield loss from weed competition, cultural operations, or misapplication of chemicals. The most critical time to control weeds in trees is from planting to early establishment, which spans from 3 to 6 years depending upon soil fertility. 

Simazine has been widely used in raspberry, boysenberry, and blueberry production (Welker and Brogdon, 1968). When used alone, broadleaf weed control has been excellent, but annual grasses and perennial weeds were not controlled in blueberry (Hertz and Wildung, 1978). Spring-planted raspberry crops do not tolerate weed competition well (Lawson and Wiseman, 1976). Simazine and diuron have been used extensively in many states in new or established cane-planted raspberry. 

Lawson, H.M. and J.S. Wiseman (1976). Weed competition in spring-planted raspberries. Weed Res., 16 155-162. 

Crop yield losses from weed competition can be substantial. The degree of loss depends on, crop and weed species present timing and duration of competitive interactions and resource availability (Agri 21 FAO, IFIC 2004 ). 

The biological basis for the above growth response is not completely resolved although relief from competition for moisture, nutrients, and light is a likely factor. The effects of weed competition on the moisture status of young pine is indicated in figure 1 (Nelson et al. 1981). 

Figure 1. Effects of weed competition on the moisture status ( ) of young pine.

I use soil solarization for crops like carrots that are the most sensitive to weed competition, and the most labor intensive to weed. Since experiential learning is the teaching style of the class, (the students learn concepts by putting their bodies to work), to answer Katie s question I ask the class to follow me back into the heat so we can get to work using this method of controlling weeds without herbicides. 

Crop yield losses due to weeds vary according to the competitiveness of the crop, the weeds present, and the population density of the weeds. Weed control is extremely important to any good program of crop production. Crop loss due to weed competition can be substantial ( 3). As an example, it has been estimated that nearly 100 million bushels of soybeans, or the equivalent of the production from 4,000,000 acres, was lost due to weed competition in the year 1970. 

Jerusalem artichoke therefore has a high tolerance of weed competition, especially when weed populations are low and comprised of relatively low growing species or those that do not develop early in the spring. Under these conditions, Jerusalem artichokes generally can be grown without the use of herbicides. 

Herbicide activity is either selective or nonselective. Selective herbicides are used to kill weeds without significant damage to nearby plants. They are used to reduce weed competition in crops, lawns, and ornamental plantings. Nonselective herbicides are chemicals that kill all plants present if apphed at an adequate rate. They are used where no plant growth is wanted, such as fence rows, ditch banks, driveways, roadsides, parking lots, and recreation areas. 

Corn needs at least 1" of water a week. Keep soil moist, but not soggy. Mulch plants to conserve moisture and cut down on weed competition. 

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