Simazine fruit crops

Finally, certain triazine herbicides can be used selectively in orchards and in some horticultural crops. In this case, selectivity is not based only on physiological differences between species, but on physical selectivity associated with the location of the herbicide and the roots of the crop and weed species in the soil. Triazine herbicides such as simazine, which has very low solubility in water, remain close to the soil surface in most mineral soils. Careful application of simazine in horticultural or fruit crops can result in the herbicide being available to control shallow-rooted weed species without harming the deeper-rooted perennial species. The success of this use is dependent not only on the relative rooting depths of the tolerant and susceptible species, but also on soil conditions and other factors that may affect herbicide fate and movement. 

In general, triazines are pre- and post-emergence selective herbicides particularly effective on annual and perennial broadleaf and grassy weeds in corn, sorghum, cotton, soybeans, sugar cane, and a host of other fruit and cereal crops. Some have anti-fungicidal properties (e.g., anilazine), and some (e.g., simazine) can be used for... 

Just as atrazine is important in com, simazine is a pre-emergence triazine that provides broad-spectrum residual weed control in many of the important fruit and nut crops when applied either alone or in combination with a contact product such as glyphosate to control weeds at the time of application (Figure 1.5). 

Although simazine was the first triazine to be developed and marketed in corn as well as other crops, the more versatile atrazine quickly became the standard herbicide in corn. Simazine, however, has remained very valuable and is important on forage crops, ornamentals, turf, and several other vegetable, fruit and nut crops, including almond, apple, artichoke, avocado, berries, cherry, citrus, grape, hazelnut, peach, and walnut. There also remains a strong demand for simazine use in corn in some areas based on specific weed pressure. Simazine is manufactured and sold by several companies today in more than 25 countries around the world, with Brazil, the United States, Australia, and Japan ranked as the top four. 

Simazine was the main product studied in early research on the triazines for weed control in tree fruits and vineyards (Doll, 1960 Larson and Ries, 1960). On mature grapevines in a deep, fine, and sandy loam soil, no differences in crop tolerance were observed between simazine and atrazine (Leonard and Lider, 1961). However, subsequent studies indicated that grapevines were more tolerant to simazine than to atrazine (Lange et al., 1969a). Prometryn was intermediate between the two in terms of crop tolerance (Lange et al., 1969a). 

Producers attempt to eliminate perennial weeds in small fruits with soil fumigation and plastic mulches. In caneberry, low rates of simazine can be used in heavier soils. Caneberry has good crop tolerance to other preemergence herbicides such as oryzalin, napropamide, and pendimethalin, though their weed spectrum may be reduced compared to simazine. 

Many triazines have been evaluated for weed control in orchards and vineyards, but primary emphasis will be placed on simazine as the herbicide of preference in most of these crops. In general, simazine is better tolerated by most tree fruits, nuts, and vines than high rates of atrazine, prometryn, propazine, terbutryn, terbuthylazine, or metribuzin. 

Trees vary in their response to simazine (Lange et al, 1969a). Walnut was the most tolerant of all deciduous fruit or nut tree species in this study, which used rates that exceeded the label use rates. Several scientists have reported increased nut quality (Larson and Ries, 1960 Neilsen and Hogue, 1992), tree growth, and leaf nitrogen from applications of simazine (Tweedy and Ries, 1966 Neilsen and Hogue, 1992). The extent of use and crops treated with simazine in California and in crops in the United States are covered in Tables 17.2 and 17.3. 

Table 17.3 Summary of simazine use on US fruit and nut crops, average for the years 2002-2005 ...

Prune and plum have less crop tolerance to simazine at high rates than the other stone fruit (Chaney et al, 1966 Elmore et al, 1970 Almoida et al, 1987). In a field experiment in California where simazine was applied for 2 years on French prune, Marianna 2624 plum rootstock, or Imperial prune on Myrobalan 29C plum rootstock, there was some phytotoxicity observed, though weed control was excellent and trunk diameter increased in most instances over an untreated check (Elmore et al, 1970). Simazine has been used with good crop tolerance at low rates for winter weeds, particularly in some of California s heavier soils. In California approximately 800 pounds of simazine were applied to 900 A of plum in 2004. 

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