Effects of spinach crop management strategies on white rust (Albugo occidentalis), leaf chlorosis, root growth and yield were evaluated in winter 1991/92. Irrigation main plots were low (I-low), medium (I-med) and high (I-high). Fungicide split-plots were none (F0), metalaxyl at planting (F1), and metalaxyl at planting plus experimental CGA 2014 foliar (F2). Genotype split-split-plots were ACX 5044 and ARK 88-354. The Gompertz model best described the white rust disease progress. At all irrigation levels, ACX 5044 had the higher rate of disease increase (rG) and earlier disease onset than ARK 88-354. Metalaxyl delayed disease onset and rG in ACX 5044 only at I-low and I-med, but not at I-high. ARK 88-354 was the least sensitive to fungicides. Yellowness and chlorosis, estimated by spectrophotometric measurements, were higher at I-med and I-high, and with F0, while ARK 88-354 had less chlorosis than ACX 5044. Root diameter was increased with F1 compared to F0. Lateral and tap root fresh and dry weights were higher for ARK 88-354. Yields for ARK 88-354 were significantly higher than ACX 5044. No treatments influenced the number of live or aphids parasitized by Pandora neoaphidis.
The effect of zero, one, and two fruits per vine on plant growth and reaction to Monosporascus root rot/vine decline were investigated. In the first study, four cultivars with differing levels of tolerance were evaluated (`Primo', `Deltex', `Caravelle', `Magnum 45'). Vine decline ratings were taken weekly during the harvest period for 4 weeks. Treatments with no fruit showed delayed and less-severe vine decline symptoms. Temperature also effected vine decline symptom expression. In a Fall test, with lower temperatures during fruit maturity, symptoms were delayed in all treatments and often absent in treatments with no fruit load. Vine decline symptom expression is greatly effected by physiological (fruit load) and temperature stress. A subsequent study was conducted to more precisely quantify the effect of various fruit loads on shoot/root partitioning and vine decline symptoms. In addition to growth parameters root disease ratings were taken. `Caravelle', the most-susceptible genotype, was grown under differing fruit loads as mentioned above in Weslaco and Uvalde, Texas. As fruit load increased, root size decreased. Increased vine decline symptoms were observed under higher fruit loads. The implications on germplasm screening and breeding for resistance will be discussed.