Recent yield advances in cotton (Gossypium hirsutum L.) hive been associated with early fruiting and high harvest index (hi). This study was conducted to examine the effects of plant density in a narrow‐row (0.76‐m interrow spacing) system on plant morphology, fruiting pattern, and yield of five genotypes that differ in degree of determinacy. ‘Acala SJ‐2’, ‘Acala SJC‐1’, and 2218, 2280, and 2086 (USDA‐ARS Shafter short‐season germplasm) were grown in a factorial design at 5, 10, and 15 plants m‐2 in 1984 and 1985. Growth data were collected four times daring the season and fruiting data obtained from plant mapping at the end of the season. Genotypes did not differ in plant height until after anthesis, when the most indeterminate genotype (Acala SJ‐2) continued vegetative growth longer than the more determinate genotypes 2280 and 2086. Increasing plant density from 10 to 15 plants m‐2 delayed maturity of the more indeterminate genotypes but had no effect on the shorter, more determinate 2280 and 2086. Genotypes 2280 and 2086 were earlier mataring than the other three genotypes regardless of plant density. Earliness was associated with a lower node number of the first fruiting branch, more rapid production of early main‐stem nodes, and increased retention of early fruiting forms. Lint yield decreased 59 kg ha‐1 for each O.l‐m increase in final plant height between 0.77 and 1.36 m when genotypes were grown at 15 plants per m‐2; at densities of 5 and 10 plants m‐2, there was no significant relationship between lint yield and plant height across genotypes and years.

Fruiting of cotton (Gossypium hirsutum L.) was evaluated by main stem node and branch position in 11 experiments over a 4-yr period to determine if mepiquat chloride (MC) (1,1-dimethylpiperidinium chloride) altered fruiting position development or retention. Fruiting events were monitored for main stem nodes 7 to 20 for first fruiting position on sympodial branches (SB1), secondary fruiting positions on sympodial branches (SB> 1), and fruiting positions on monopodia) branches (MD). Ten consecutive plants were plant mapped from each of four replications in each experiment and combined as a 40-plant total for analysis of treatment and node effects using experiments as replications. Mepiquat chloride was applied at 49 g ha-1 when average plant height was 0.57 m and plants averaged 0.9 white blooms m-'. Summed across nodes, plant zones SB1, SB>1, and MD accounted for 60, 26, and 13% of all harvestable bolls, produced 37, 46, and 17% of all fruiting positions, and set 45, 16, and 23% of all fruiting positions as harvestable bolls, respectively. Application of MC did not increase total number of bolls. The interaction of MC treatment and nodes was significant for SB1 and SB> 1, with MC treated plants setting more bolls at lower nodes but fewer at upper nodes. The maximum cumulative benefit occurred at node 12 where MC treated plants had 15% more bolls matured than control plants (58.3 and 50.6 bolls m-', respectively). This advantage from MC treatment was not maintained as upper nodes matured fewer bolls than control plants. Plants treated with MC produced 3.1% fewer (P = 0.07) fruiting positions than control plants (288 and 279m-2 , respectively). Treatment by node interactions were significant for SB1 and SB> 1, with MC increasing fruiting positions up to node 15 at SB1 and up to node 9 for SB> 1, but having fewer at the remaining nodes. Early boll load was stimulated by MC. Late season boll load was decreased, apparently not by limited initiation of fruiting positions, but rather by increased abortion of fruiting forms. Use of MC according to the rate and timing of these tests would be of benefit when length of the season is a primary constraint to yield potential. In full-season, non-rank cotton, however, the early benefit in boll load is lost.

Interest in production of narrow‐row cotton (Gossypium hirsutum L.) is increasing. Plant characteristics considered important for cultivars grown in 1‐m row spacings may not be the same for plants grown in 0.76‐m spacings. This field study was conducted to determine the influence of genotype and plant density on accumulation and allocation of dry matter in a narrow‐row production system. Five genotypes representing a wide range in size and growth habit were grown in factorial tests at 5,10, and 15 plants m‐2 at the U.S. Cotton Research Station in Shatter, CA, in 1984 and 1985. Growth measurements were made four times during each season. Increasing plant density increased mean leaf area index (LAI) and total dry matter of genotypes at all sample dates but decreased harvest index (HI) from 0.58 to 0.53 at maturity. Genotypic differences in LAI and total above‐ground dry matter became apparent only after anthesis. Mean season‐end dry matter ranged from 9.78 Mg ha‐1 for the short determinate genotype 2086 to 10.88 Mg ha‐1 for ‘Acala SJ‐2’. Final mean HI ranged from 0.66 for 2086 to 0.47 for Acala SJ‐2. Height and vegetative growth rates (HGR and VGR) per 100 heat units (HU) were closely negatively associated with fruit growth rates (FGR) between the June and August sample dates. Including leaf area growth rate (LAGR) with FGR as a FGR/LAGR ratio as the independent variable improved r2 from 0.59 to 0.81 for HGR and from 0.69 to 0.90 for VGR. Node growth rate (NCR) was only minimally sensitive to the FGR/LAGR ratio. These results show that vegetative development during early fruiting is related to size and earliness of the reproductive sink and growth rate of the source. Cultural practices that are presently used for cultivars with a low FGR/LAGR ratio may not be ideally suited for more determinate cultivars with a high ratio.

Emergence of cotton (Gossypium hirsutum L.) seedlings was related to seed quality and temperatures following planting in a 3‐yr field study at Shafter, CA. Environmental conditions for seed production were selected to provide a broad range in seed quality. Seed quality, as determined by the standard germination test and the cool test, was combined with heat units (HU) after planting for predicting field emergence percentage. A total of 74 seed lots (11 in 1984, 39 in 1985, and 24 in 1986) were planted at two different dates, and emergence of 100 seed from each of four replications evaluated. Warm germination percentage (W%) was measured at 30 °C, and ranged between 25 and 90%, cool germination (C%) was measured at 18 °C, and ranged between 1 and 88%, and field emergence percentage ranged from 5 to 98% in these studies. Multiple regression was used to determine the degree of association between variables. Predicting field emergence with C + W% was better than either component alone (r2 = 0.352 for n = 148). The HU (base 60 °F) for 5 or 10 d after planting explained as much variation in field emergence as seed quality (r2 = 0.348 and 0.365), but HU 15 d after planting were not related to field emergence. When HU 5 d after planting, C + W% percentage, and the interaction between the two were considered in multiple regression, 68.5% of the variation in field emergence was explained. With 10 HU 5 d after planting there was a linear increase in field emergence percentage as C + W% increased, but at 25 HU, seed with C + W% of 110 had as many seedlings emerge as lots with C + W% of 175. Eliminating seed lots with warm germination percentages less than 80 from these regressions did not alter the predicted values for field emergence within the range of the data, but did reduce the statistical significance of the relationship. The HU for 5 d can be forecast on the National Oceanic and Atmospheric Administration's (NOAA) weather radio with reasonable accuracy in the San Joaquin Valley of California. If temperatures can be forecast accurately in other regions, cotton growers can adjust seeding rates and plant to a desirable stand, if warm and cool germination percentages of planting seed are known.

Chemical defoliation is a necessary pre‐harvest practice in cotton (Gossypium hirsutum L.) production in California, and all harvest aid efforts require proper timing to preserve cotton lint yield and quality. Generally, cotton growers are advised to begin defoliation as early as possible, but not so early that they cause yield and quality loss. In order to have confidence in this final pre‐harvest step, growers monitor the growth stage of their crop by counting the number of nodes above cracked boll (NACB). In California, it is common practice to apply the first defoliant treatment at 4 NACB, which corresponds with the US Cotton Belt's recommended timing, which is when 60% of the harvestable bolls are open (9,20). It can be beneficial to have an early defoliant application because often it leads to an earlier harvest. This early harvest allows cotton growers to conduct their harvest prior to the onset of adverse late‐season fog or rains that can occur in California's San Joaquin Valley and make harvests more difficult. The objective of this research on San Joaquin Valley Acala cotton was to compare the impact of different rates of Ginstar (thidiazuron/diuron) or Ginstar plus Finish (ethephon/cyclanilide) on defoliation, yield, and fiber quality of cotton when defoliant applications were initiated at the earlier 6 NACB timing, which corresponds to 40% open boll versus the common 4 NACB timing. Starting the defoliation process with an Acala cultivar at 6 NACB instead of at 4 NACB did not significantly affect yield or cotton HVI (high volume instrument) fiber quality characteristics. Earlier defoliation could be of significant benefit in years when later‐maturing crops or worsening harvest‐season weather necessitate the initiation of an earlier harvest.