More than 10 Sub1 rice varieties carrying the submergence-tolerance gene have been released for flood-prone environments in tropical Asia. Improved management practices have been shown to enhance yields of these varieties. The objective of this study was to dissect the growth response of IR64-Sub1 to integrated crop management in a flash flood at the late vegetative stage. Field experiments were conducted at the International Rice Research Institute, Philippines in the dry and wet seasons of 2013. Complete submergence was imposed for 14 days starting at 37 days after transplanting. Integrated management practice (IMP) consisting of: (i) application of fertilizer (compared with no fertilizer use in conventional practice), (ii) use of lower seeding rate (400 vs. 800 kg ha−1) in the nursery bed, (iii) use of slightly older seedling for transplanting (30 vs. 18 day-old), and (iv) higher planting density (33.3 vs. 25.0 hills m−2) gave yields higher by 8–87% compared with the conventional practice (1.3–2.4 t ha−1) in both seasons. This was attributable to higher shoot biomass after water recession, more tillers m−2, greater leaf area expansion and shoot biomass accumulation during the recovery period, and higher filled-grain percentage at maturity. The improved management had no positive effect on panicle formation, spikelets panicle−1, and harvest index since stress was imposed at the transition period between vegetative and reproductive phases. Our results suggest the appropriate nursery management, for submergence-resilient seedlings to further alleviate damage caused by flash floods and increase the yield of Sub1 varieties in flood-prone rainfed lowlands.

Broomrape is a severe problem in the continuous cropping of bidi tobacco in India. Fifteen herbicides were evaluated for postemergence control, at different dates and rates, in field experiments in Nipani, Karnataka State. The effects of the herbicides on Orobanche control and growth and yield of tobacco were compared to the effects of handweeding and an untreated check. Following this screening experiment, four herbicides were selected for further testing. Glyphosate at 500 g ai/ha applied at 60 days after transplanting (DAT) and imazaquin at 10 g ai/ha applied at 30 DAT reduced the number of aboveground broomrape spikes by 75 to 80% and increased the tobacco yields by 80 to > 100% compared to the untreated plots. Imazethapyr and EPTC were found to be less effective for broomrape control, but they still led to substantially higher tobacco yield. None of the herbicide treatments resulted in yields higher than those in the hand-weeded plots. These plots probably did not yet reflect the potential yield of tobacco under broomrape-free conditions, due to nonemerged spikes. Toxicity to tobacco of all herbicides was higher for the higher rates tested. It was lowest with imazaquin.

Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2 linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.

Experiments were conducted to investigate the possibility that rhizobacterial nodulation in legumes influences parasitic attack by broomrape. Small broomrape (Orobanche minor), which is commonly associated with swellings of the host root, was studied on red clover (Trifolium pratense) in the presence or absence of Rhizobium leguminosarum bv. trifolii inoculum and was compared to Egyptian broomrape (Orobanche aegyptiaca), which is not associated with host root swellings. Small broomrape showed greater percent seed germination and formed a greater number of attachments on red clover inoculated with rhizobacteria in comparison with noninoculated plants. In contrast, inoculum did not appear to enhance Egyptian broomrape seed germination or the number of its attachments on the host roots compared to noninoculated controls. In aseptic culture, the addition of Rhizobium increased the success of small broomrape in parasitizing clover but was not essential for parasitization. No rhizobacteria were detected in cultures derived from tubercles under septic or aseptic conditions. Morphological observations of small broomrape attachments on red clover suggest that parasitic attachments were not situated over the bacterial nodules but may involve parasite-induced protrusion of host plant root cortex. These results indicate that although rhizobacterial nodulation is not required for parasitization, the presence of nodules facilitates small broomrape germination and attachment to red clover.

A replacement series study was conducted to describe the aggressivity between cucumber, smooth pigweed, and livid amaranth. Cucumber was three times more competitive than smooth pigweed or livid amaranth, under the conditions of this study. However, there was equal competition and no antagonism between smooth pigweed and livid amaranth. Where cucumbers were planted in mixture with either of the two weeds, the relative yield total values were approximately 10 to 20% higher than the monocultures. Cucumber was a superior competitor when grown in mixture with smooth pigweed or livid amaranth, and the following aggressivity hierarchy exists: cucumber > livid amaranth = smooth pigweed. Results from the additive field study indicated that amaranth dry weights were significantly affected by smooth pigweed and livid amaranth density. Dry weight of amaranth was decreased by 48% at Gainesville and 25% at Live Oak, at 18 plants/m2. Despite differences between the Gainesville and Live Oak results, the dry weight data were similar for both smooth pigweed and livid amaranth at each location.

Multiple means of overcoming interspecific competition between transplanted cabbage and interseeded cover crops were studied in field trials conducted from 1995 to 2001. Cover crop species and time of seeding (1995 and 1996), use of supplemental nitrogen (1997 and 1998), and herbicide regulation (1999 and 2001) were evaluated with the objective of integrating soil-improving cover crops into cabbage production while facilitating weed suppression with minimal use of herbicides. Cabbage was cultivated at 10, 10 + 20, or 10 + 20 + 30 d after transplanting (DAT) with or without cover crops (hairy vetch, lana vetch, or oats) sown at the time of the last cultivation. Early interseeding (10 DAT) of all species significantly reduced cabbage yields. Both vetches could be sown 20 or 30 DAT without a yield penalty. However, weed suppression was not consistently greater than cultivation without cover crops. Spring oats were unacceptably competitive, even when sown 30 DAT in some years. With additional nitrogen, cabbage yields were consistently increased, but the increases were not directly related to decreased competition from either weeds or cover crops. The potential for herbicide regulation of cover crops to prevent cabbage yield losses could not be evaluated because cabbage yields were not reduced by cover crops in 1999 and 2001. Although interseeded crops did not generally provide significant in-season weed suppression compared with cultivation alone, the lack of yield penalty and the potential soil-improving qualities of legumes may justify interseeding hairy vetch at 20 DAT in an integrated system.