The Effect of Variable Rate Irrigation on Banks Grass Mite, Oligonychus pratensis (Banks), and Southwestern Corn Borer, Diatrea grandiosella (Dyar) Populations in Corn

(Fields 5D and 5E)
Ed Bynum, Sally J. Officer, Jill D. Booker, James P. Bordovsky, Eduardo Segarra, Robert J. Lascano and L. T. Wilson

Fig. 1. Block locations and grain yield across the crop management zones and uniformly watered field.Objectives: The objectives were to:

1. Describe the effects of site-specific water, nutrient, and pest management on growth and production in an irrigated corn system in rotation with cotton.

2. Quantify the economic and environmental cost-benefit of managing multiple stresses in site-specific compared to conventional systems.

Methodology: Four Crop Management Zones (CMZ) based on soil texture and slope were established. Normal cultural practices were uniformly applied across both fields. Banks grass mite, Oligonychus pratensis (Banks), populations were monitored in eight blocks located in two fields (Fig. 1). Four blocks were located in the uniformly watered field (conventional farming) and four in the crop management zones (site-specific farming). Weekly mite damage ratings were taken from 11 July to 8 August. Southwestern corn borer (SWCB), Diatrea grandiosella (Dyar), infestations were monitored on 4-5 September after an aerial spray of Asana (5.8 oz/ac) was applied on 26 July across the two fields. Yield was calculated from hand-sampled ears harvested from each block. Yield monitor data was also collected.

Results: Mite damage was statistically lower in the CMZ B80 and CMZ B80-20 than the conventionally farmed field (Table1). The CMZ B80-20, showed statistically higher SWCB infestation and lower yield than the conventionally farmed blocks and the other CMZ’s. Pest infestations vary within and between growing seasons, therefore, multiple years of data are needed to correlate factors that affect economic thresholds in site-specific farming.

Table 1. The effect of conventional and crop management zone (CMZ) farming systems on cumulative mite damage days (CMDD), percentage Southwestern corn borer infestation and grain yield at Helms Farm, 2002.

Farming System Irrigationb Block CMDDa Infestation (%)a Yield (lb/ac)a
Conventional  B80  1  61.5 c  5.0 c  7989.0 ab
Conventional  B80  2  72.5 ab  10.6 bc  7981.0 ab
Conventional  B80  3  69.1 abc  8.8 c  8433.0 ab
Conventional  B80  4  78.3 a  16.6 b  6864.0 c
CMZ  B80+20  5  64.5 bc  6.9 c  8543.0 a
CMZ  B80  6  51.5 d  8.1 c  8019.0 ab
CMZ  B80  7  45.2 d  7.5 c  7691.0 b
CMZ  B80-20  8  43.5 d  31.6 a  5310.0 d
aColumn values followed by different lower case letters are statistically different, P<0.05, (Duncan’s new multiple range test)
bB80=base rate of 80% ET, B80+20=80% ET + 20% additional water, B80-20%=80% ET-20% water

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