ROW SPACING & PLANT POPULATION AS IPM TOOLS FOR NO-TILL SILAGE CORN IN CENTRAL CALIFORNIA Anil Shrestha Statewide IPM Program University of California Kearney Ag. Center, Parlier Carol Frate University of California Cooperative Extension Tulare County Charles Summers University of California, Davis

Conservation Tillage (CT) in California CT is fairly new for California Less than 2% of annual crop acreage In California, CT focuses more on reducing number of tillage passes than on preserving surface residues.

Reasons for low adoption of CT in California Lack of locally available CT equipment and information Inexperience with CT techniques Predominance of surface or gravity irrigation systems Tillage-intensive systems developed for several decades are highly productive Diversity of crop types and cropping systems

Current Interest in CT in California NRCS Environmental Quality Incentives Program (EQIP) Rising fuel prices Conversion to overhead irrigation systems Extension activities of CT Workgroup Environmental regulations Opportunities for triple cropping*

CT activity is fairly limited to Research/Demonstration by CT Workgroup with grower partners However, there is new interest in CT ……

Coupling overhead irrigation systems with CT: A means for optimizing cheap, efficient and resource-conserving production systems?

California Waste Discharge Permit Requirement General Order 55-2007-0035 for Milk Cow Dairies -Limits field application of dairy waste nutrients to 140% of expected crop uptake

Dairy forage triple-cropping as a means to increase forage production and nutrient uptake Nutrients can be applied to the third crop, planting of which is enabled by CT

Harvesting winter forage wheat, strip-tilling and planting corn, Tipton, CA, May 2005

Strip-till planting corn in wheat residue

Strip-till planting corn in wheat residue

No-till planting sorhgum-sudan in corn residue

Post-plant irrigation of sorhgum-sudan

conventional tillage + furrows for irrigation Traditional corn – conventional tillage + furrows for irrigation

Factors enabling CT Planting equipment that can do different spacings GPS and flat planting No tractors in the field Irrigate flat – no furrows Pesticide application by air Harvest equipment that is flexible

Studies elsewhere have found that: Narrow rows (38 cm) and higher corn density reduced the need for long-term residual herbicides Corn yields increased by 10-15% in narrow rows HOWEVER, these results have not been consistent. Climatic conditions, rainfed cropping systems, dominant weed species have influences

Rationale Narrow rows close canopy earlier then the wide rows and shade later-emerging weeds Germination of some weed seeds that require light may be prevented or reduced by shading Increased crop density may help the crops compete better for resources Light levels under the crop canopy may influence insect pest dynamics

Objective Evaluate the effect of corn row spacing (38 vs 76 cm) and plant population (69000, 86000, 104000 plants ha-1) on light attenuation patterns, weed populations, insect dynamics, and crop yield

Experimental details Harvested winter forage Planted May 13 & 14th , 2004 & 2005 Variety: DK C66-80 (RR) 10 row JD No-Till Planter, used GPS Split-plot with row spacing as main plot and plant population as sub plots 4 replications Plot size – 7.6 m by 402 m Glyphosate aerially applied in June Mechanically harvested in September

Measurements Weekly measurements on PAR above and below the corn canopy Stalk diameter Weed populations mid-season & at harvest Weed biomass at harvest Insect (corn leaf hopper, aphid, leafminer) Crop yield

Results

Distribution of weed species in June (before herbicide application)

Light interception by corn canopy 2004 W = 76 cm N = 38 cm L = 69000 M = 86000 H = 10400

Light interception by corn canopy 2005 38-cm rows closed canopy 6-13 days earlier than the 76-cm rows

Weed densities- July 2004 Spacing P = 0.10 Population P = 0.95 Spacing*Pop P = 0.55

Weed densities- July 2005 Spacing P = 0.005 Population P = 0.03 Spacing*Pop P = 0.0005

Weed biomass at corn harvest 2004

Weed biomass at corn harvest 2005

Narrow-rows suppressed weeds better than wide-rows 76 cm 36 cm

Insects monitored Monitored June to August using sticky traps Corn leafhopper (Dalbulus maidis) Corn leaf aphid (Rhopalosiphum maidis) Monitored June to August using sticky traps Corn leafminer (Agromyza sp.)

Insect population dynamics Plant populations affected insect populations but row spacing did not Corn leaf hopper densities were about 3/card in the high corn population plots compared to 6-7/card in the low population plots Aphid numbers were about 80/leaf in low population plots compared to <50/leaf in high population plots Leafminer populations were 2-3 times greater in the low corn population plots compared to the high population plots

Corn dry matter yield Adjusted to 70% moisture

Stalk diameter 76-cm rows 38-cm rows 2004 - 2.4 cm 2.6 cm 2.4 cm P = 0.01 P < 0.001

Conclusions Preceding crops in the rotation may be the predominant weed in no-till systems 38-cm rows intercepted more light and closed canopy 6-13 days earlier than the 76-cm rows Weed density at mid-season was lower in the 38- than the 76-cm rows in one year of the study Weed biomass at the end of the season was lower in the 38- than in the 76-cm rows in both years Plant population had no effect on light interception or weed dynamics

Conclusions Insect populations were lower in the high plant population plots regardless of row spacing Corn stalk diameter was greater in the 38- than in the 76-cm rows Crop yield was not affected by row spacing or plant population Some caveats: - Dairy growers usually rely on custom applicators for herbicide treatments so early canopy closure may not be desirable for aerial application of a herbicide like glyphosate - Growers do not see any immediate benefit to growing corn in 38-cm rows but some are interested in twin-rows