This review describes the differences in weed management that must be addressed when plastic culture is added to the production cycle. Three specific areas are addressed: weed management under plastic mulch, weed management between plastic mulch, and weed management under row covers.
Two field experiments were conducted during 1981-1982 to determine the feasibility of using midday canopy temperatures, measured with an infrared radiation thermometer, for irrigation scheduling in ‘Oregon 1604’ and ‘Galamor’ snap beans (Phaseolus vulgaris L.) Treatments which allowed various levels of positive canopy minus air temperature differences [stress-degree-days (SDD)] to accumulate between irrigations were evaluated along with a treatment irrigated at 4 growth stages, a dry treatment, and a control treatment which was irrigated at -0.06 MPa soil water potential (SWP). Diurnal measurement of canopy and air temperatures indicated that the greatest differences between canopy and air temperature occurred near solar noon. In 1981, all treatments irrigated by an accumulation of positive SDD had reduced yields compared to the control SWP treatment. In 1982, under higher rainfall and lower air saturation vapor pressure deficits (VPD) than in 1981, yields of the SDD irrigated treatments were comparable to those obtained with the SWP treatment. Accumulation of positive SDD values to schedule irrigations was adequate when midday VPD values were low. However, when high VPD occurred, SDD values were always negative. A model is presented in which SDD values can be adjusted for environmental variability to more accurately schedule irrigations. Measurements of air temperatures within the canopy were made and compared to surface canopy temperatures measured with an infrared thermometer. Regression analysis showed that canopy temperature could be predicted using the air temperature within the canopy (R2 = 0.89). The sum of SDD values for the season was used to estimate canning maturity pod yield (R2 = 0.65).
Field experiments were conducted to evaluate the effects of differential irrigation treatments on the yield and pod quality of ‘Oregon 1604’ and ‘Galamor’ snap beans (Phaseolus vulgaris L.) in 1981 and 1982. Treatments in which various levels of positive canopy minus air temperature differences [stress-degree-days (SDD)] accumulated between irrigations were evaluated along with irrigation at 4 growth stages, a dry treatment which received only one irrigation to establish plants, and a control treatment irrigated at -0.06 MPa soil water potential (SWP). In both seasons, yield was related strongly to the average soil water potential from planting to harvest. Yields in 1982 were at least 5 MT/ha greater at a given average soil water potential than in 1981. Yields of ‘Oregon 1604’ and ‘Galamor’ were similar under adequate irrigation, but under greatest water stress, yield of ‘Oregon 1604’ was higher than for ‘Galamor’. Pod number was reduced only in the dry treatment. Percentage of set pods, pod length, and number of seeds per pod were all reduced by low irrigation, while fiber content of pods and weight per seed were increased by low irrigation.
Two field experiments were conducted to evaluate the effects of differential irrigation on plant growth, development, and water status of 2 snap bean cultivars, ‘Oregon 1604’ and ‘Galamor’ (Phaseolus vulgaris L.). Plants were grown at various irrigation levels ranging from a well-watered control to a dry treatment which received only one irrigation to establish plants. Measurements on plants sampled weekly at 6 times during the growing season showed that total plant dry weight, total leaf dry weight, total leaf area, average area per leaf, and number of leaves per plant were reduced by water deficits in both cultivars. Also, for both cultivars, total leaf area per plant was reduced more by a decrease in area per leaf than by a reduction in leaf number. Specific dry leaf weight was higher in the drier treatments. During each year, a significant difference between treatments occurred earlier in the season for total leaf area per plant than for total plant weight. At predawn, leaf water potential (ψ) always was more negative in the dry treatment than in the control. Early in the season, there was no significant difference in midday ψ between the control and dry treatment. Later, as soil water became limiting, the dry treatment had a more negative ψ than the control. Near the end of the season, after the dry treatment had been subjected to a long period of water stress, midday ψ was more negative in the control than in the dry treatment. Although some osmotic adjustment occurred in the dry treatment, leaf turgor potential (ψp) was generally lower than in the control throughout the day. As ψ decreased from early morning through midday, transpiration rates increased due to an increase in evaporative demand on the leaves. Leaf diffusive resistance also increased with decreasing ψ but a “threshold value” for stomatal closure was not demonstrated.
Field studies were conducted in 1984 and 1985 to document the effects of plastic mulches and row covers on soil and air temperatures and yield of muskmelons (Cucumis melo L.) in North Carolina. Treatments included bare ground, black plastic, and clear plastic, each with and without a slitted clear plastic row cover. In addition, both trickle and overhead sprinkler irrigation were evaluated. Soil temperatures were increased by plastic mulches, with clear polyethylene resulting in the highest soil temperatures. Air temperatures were increased by row covers. In 1984, total and early yields were increased over bare ground plots with the use of either clear or black polyethylene mulches. Row covers did not influence yields. In 1985, a warmer year than 1984, no total yield increases resulted from use of either row covers or mulches; however, row covers and clear plastic mulch increased early yield. Trickle irrigation used less water than did overhead irrigation, but did not increase yields.
Chemical defoliation of cucumber (Cucumis sativus L.) vines was evaluated as a method for rapid screening of breeding lines. Six chemicals (dinoseb, diquat, ethephon, glufosinate, glyphosate, and paraquat) were used at one or 2 rates on one pickling and one fresh-market cucumber cultivar (‘Calypso’ and ‘Poinsett 76’, respectively) in 1983 to determine speed of vine defoliation and amount of fruit damage. Of the chemicals tested, paraquat at 0.6 kg/ha provided the most rapid defoliation (85% to 91% defoliation one day after treatment) but caused some bleaching and chlorosis of the fruit. If the fruit were rolled 180° during evaluation, the damage was not noticeable. Chemical defoliation of vines for simulated once-over harvest provided a rapid, labor-saving method, requiring only 42% of the time to evaluate each plot compared to the conventional method. The chemical defoliation method is especially useful for initial evaluation of populations and breeding lines for fruit yield and other horticultural characteristics.
Seventeen herbicide treatments used in the production of sweet potato [Ipomea batatas (L.) Lam.] seed roots were evaluated for their influence on transplant production the following season. Number of transplants/root at five harvests, total transplants/root, and transplants/100 g of root were not influenced by the herbicide treatments. Weight/transplant was influenced by the herbicide treatments only at the last harvest. Total transplant weight/root and total transplant weight/100 g of root also were not influenced by the experimental treatments. No visual deleterious effects on transplant production were observed with any of the herbicide treatments.
A commercially available cryoprotectant (50% propylene block copolymer of polyoxyethylene, 50% propylene glycol; trade name FrostFree) and an antitranspirant (96% di-1-p-menthene, i.e., pinolene, a terpenic polymer, 4% inert; trade name Vapor Gard) were evaluated for their ability to protect `Pik Red' tomato (Lycopersicon esculentum Mill.) and `Keystone Resistant Giant #3' pepper (Capsicum annuum L.) plants during frost and freeze occurrences in the field. Tests were conducted during four spring and two fall seasons. Protection from these products was not observed under field conditions when minimum air temperature reached -3.5C and -l.0C on separate occasions. Yields for treated and untreated plants were similar. Neither cryoprotectant injured the foliage in the absence of cold events.