In the fall of 1990, a new form of whitefly, tentatively identified as the poinsettia strain of Bemisiatabaci (Gennadius), was introduced into the agricultural regions of the desert southwest. Large densities of whitefly nymphs developed on cruciferous crops and substantial increases in pesticides for whitefly control were used. After overwintering in active stages on these crops, whiteflies moved into spring cantaloupes and developed moderate populations levels in some fields. In March, whiteflies migrated to newly-planted cotton and developed huge densities by August. At this time emerging fall cantaloupe was attacked and over 95% of this crop was destroyed by whitefly feeding. Whiteflies also developed to damaging numbers on alfalfa, grapes, citrus, crops not known to host the cotton strain of B.tabaci. Population densities remained high through the fall crucifer and lettuce seasons causing crop losses and delayed maturity. Damage estimates presently rest at roughly $122 million.
Thirty-one cultivars of muskmelon (Cucumis melo L.) were evaluated for their response to foliar dusting sulfur applications. Most cultivars were highly resistant to sulfur injury. Resistance was variable among cantaloupe types (Reticulatus group); all winter melon types (Inodorus group) were resistant.
A seedling disorder of broccoli (Brassica oleraceae L. var. italica) characterized by chlorotic cotyledons and delayed seedling growth is described. This disorder, termed “yellow cotyledon”, has been observed in field plantings under high temperatures with some broccoli seed lots. Yellow-cotyledon disorder can be observed in laboratory germination tests if they are conducted under illumination, where unaffected seedlings will develop green cotyledons. Little relationship was found between overall seed vigor and the expression of yellow cotyledon by use of early germination counts and accelerated aging tests, although the most severely affected seed lots had been stored for several years. Field trials in 2 years showed that although seedlings with yellow-cotyledon disorder developed into normal plants, maturity was delayed and total yields were reduced.
Lettuce (Lactuca sativa L. ‘Empire’) seeds (achenes) were given an osmotic priming treatment (24 hr in aerated —1.5 MPa polyethylene glycol (PEG 8000) solution at 18°C in the light) which alleviated thermodormancy in laboratory tests. The seeds then were coated commercially for precision planting. Additional seeds also received a proprietary treatment for enhancing high temperature germination (Royal Sluis Split-kote D). In field trials in the Imperial Valley of California, where the soil temperature exceeded 35°C for the first 11 hr of imbibition under sprinkler irrigation, total emergence of untreated seeds after 6 days was between 18% and 21%, whereas that of primed and Splitkote D seeds ranged from 46% to 69%. Uniformity and rate of emergence were also greater for the primed seeds, with 91 % of the final emergence occurring by the 3rd day, as compared to only 70% for the control. Seed priming prior to coating can be an effective method of improving lettuce stand establishment under high temperature conditions.