Seeds of the commercial cultivar for seedless watermelons, TriX313, were separated into groups based on thickness in one experiment and on weight in another. Number of triploids and tetraploids were recorded for each category. There were no significant differences in ploidy levels based on either weight or seed thickness. Seeds from this same cultivar were treated with priming solutions of polyethylene glycol (PEG 8000), KNO3, and distilled water for three lengths of time (1,3, or 6 days). The seed was subsequently air-dried for 1 or 7 days and then tested for germination and emergence.

A field experiment with subsurface drip irrigated watermelon was conducted on a Casa Grande s.l. soil at the Maricopa Agricultural Center in 1992 to evaluate the field performance of two slow release nitrogen (SRN) fertilizers in comparison to a conventional soluble N source, urea, ammonium- nitrate (UAN-32). Single, preplant applications of 0, 100 and 200 lbs N/acre supplied from methylene urea (Nutralenes) or 100, 150 and 3(X) lbs N/acre from a methylene urea-ammonium sulfate mixture (MUAS) were evaluated in comparison to treatments of UAN-32 containing from 52 to 445 lbs N/acre made in five split applications. Yield response to N rates above 100 lbs/acre were similar for all three N sources, indicating that a single, preplant application of a suitable SRN material at an adequate rate could provide N efficiently over the entire growing season. The highest numerical yield (49.3 tons/acre) was obtained with a N rate of 150 lbs N/acre from the MUAS material. Monitoring of petiole nitrate levels throughout the season indicated that N release from the MUAS was more rapid and more complete than from the methylene-urea product. At suboptimal N rates, i.e. < 150 lbs N/acre, split applications of UAN-32 appeared to be somewhat more efficient than the slow-release products.

Rising water costs and concern for groundwater contamination are driving growers to improve irrigation and fertilization efficiency. A tentative Best Management Practice (BMP) for nitrogen fertilization of watermelon, a high water and nitrogen fertilizer use crop, has been developed, but needs further field verification. Information from tensiometers is used to schedule irrigations and watermelon petiole nitrate levels at critical growth stages are used to recommend rates of nitrogen fertilizer to apply with the objective of producing economic yields while limiting conditions which favor nitrate leaching to groundwater. In 1991, a field experiment consisting of a complete 3x4 factorial arrangement of soil moisture tensions, -12, -7 and -4 kPa, and 60, 214 315 and 500 kg N/ha, respectively, applied through a subsurface trickle irrigation system to watermelon was conducted on a Casa Grande sandy loam at the Maricopa Agricultural Center. Petioles were sampled from the youngest mature leaf beginning at the 3-4 leaf stage and then at major growth stages until first harvest. Harvested melons were weighed and soluble solids, dry matter and N uptake were determined on two representative melons from each experimental unit. An estimate of vine dry matter and N uptake was also determined. Soil samples were taken at 30 cm depth intervals to 1.2 m and analyzed for extractable N. A trench profile method was used to determine root distribution patterns for the three soil moisture treatments receiving optimum N. Petiole nitrate levels were highly responsive to N fertilizer treatments and accurately quantified visual observations of crop N status. Petiole nitrate results also indicated that the preliminary tissue nitrate test was adequate in assisting with a nitrogen management program though minor modifications were necessary. Marketable yield showed a tension x N interaction with a ridge of maximum yield occurring from high soil water tension and low N to low soil water tension and high N with yield reductions on either side of the ridge. Yield estimates along the ridge ranged from 101 Mg/ha (45.4 ton /ac) at -8 kPa tension and 280 kg N/ha to 105 Mg/ha (47.3 ton /ac) at -4.4 kPa tension and 376 kg N/ha. A cost return analysis determined that maximum economic returns were $12,059/ha when 311 kg N/ha were applied in conjunction with -6 kPa soil tension (145 cm water). Unaccounted for N, as determined by an N balance method indicated large amounts of N were unaccounted for when high rates of N were applied under wet soil conditions. N loss was concluded to be due to either leaching and/or denitrification under these conditions.

A commercial product called Beescent® containing a mixture of chemicals including chemicals used by honey bees as pheromones, was applied to watermelons in early bloom on Aug. 15, 1991. Honey bee visitation to treated, 18-row plots, were significantly higher than to untreated for only 2 days, the day of treatment and the next day. Watermelon yields were not effected. The daily high temperatures reached 86-88 °F, so that most of the chemical had volatilized away by the end of the first day.

Calsweet' watermelons were irrigated at three levels using a drip irrigation system. Number and weight of melons were recorded for three harvest dates. The low water treatment had significantly lower average melon weight than the medium and high treatments. There were no significant differences between the number of melons produced for each treatment.

No description available.

A study was made of the response of six kinds of melons to different nitrogen fertilizer rates when grown with drip irrigation. Results indicated a general response of petiole nitrate and yields to increasing N rates, depending on the kind of melon. The study will be continued in 1990 and include water and N rates with three kinds of melons.

Five insecticides, four oils, one soap, and two insect growth regulators were evaluated for control of sweetpotato whitefly on muskmelons and watermelons in 1990. Best control (> 80%) was noted from the insect growth regulators at 11 days post treatment, but declined thereafter. Oils as a class provided some control but not all oils provided similar results. Insecticides tested did not provide adequate control and resulted in increased whitefly egg and nymph numbers at 11 days post treatment.

Seedless watermelons have become an important commodity in Arizona. In 1991 16 cultivars were compared and evaluated at the Maricopa Agricultural Center. Tri-X 313 had overall good performance and remains the standard. Several other cultivars show promise.

Calsweet watermelons were irrigated at two levels, utilizing a drip irrigation system for accurate rate measurements. Number and weight of harvested melons were recorded for four harvest dates. There were no significant differences in weight per melon, number of melons and total mean weight for the water treatments within the four harvest dates. For the entire season, number and total weight of melons were higher in the wet treatment; the weight per melon was higher in the dry treatment.