Wayne E. Mitchem

Tree Growth, Fruit Size, and Yield Response of Mature Peach to Weed-Free Intervals

An experiment was conducted at one location in 1999 and two locations in 2000 to determine the critical weed-free period for peach in North Carolina. The cultivars for the three locations were ‘Contender’, ‘Norman’, and ‘Summerprince’. Weed-free intervals of 0, 3, 6, 9, 12, and 15 wk after peach tree bloom were established. Paraquat at 1.1 kg ai/ha plus nonionic surfactant at 0.25% v/v was applied every 10 d, after treatments were initiated at peach bloom, to maintain weed-free plots. Large crabgrass, hairy vetch, and smooth crabgrass were the primary weeds in Contender. Horseweed, smooth crabgrass, and large crabgrass were the primary weeds in Norman. Bermudagrass, smooth pigweed, and common lambsquarters were the primary weeds in Summerprince. No differences in trunk cross-sectional area were observed between the weed-free periods. Maintaining the orchard floor weed-free for 12 wk after peach tree bloom resulted in the greatest fruit size (individual fruit weight and diameter), total yield, and fruit number. Nomenclature:Paraquat, bermudagrass, Cynodon dactylon (L.) Pers. CYNDA, common lambsquarters, Chenopodium album L. CHEAL, hairy vetch, Vicia villosa Roth. VICVI, horseweed, Conyza canadensis (L.) Cronq. ERICA, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, smooth crabgrass, Digitaria ischaemum (Schreb.) Muhl. DIGIS, smooth pigweed, Amaranthus hybridus L. AMACH, peach, Prunus persica (L.) Batsch., ‘Contender’, ‘Norman’, and ‘Summerprince’

Response of Five Summer-Squash (Cucurbita pepo) Cultivars to Halosulfuron1

Response of ‘Dixie’, ‘Lemondrop’, ‘Multipik’, ‘Superpik’, and ‘Seneca Prolific’ summer squash to halosulfuron PRE or POST at 0.036, 0.053, and 0.072 kg ai/ha, or halosulfuron PRE fb halosulfuron POST at 0.018 fb 0.018, 0.027 fb 0.027, and 0.036 fb 0.036 kg/ha was field evaluated in 1997 and 1998. All halosulfuron treatments and rates reduced the height of cultivars 17–19% at 6 WAP (weeks after planting) and summer-squash injury (chlorosis and necrosis of crop foliage) was 6, 14, and 11% from halosulfuron PRE, POST, and PRE fb POST, respectively. Early summer-squash flowering was reduced 32–82% by halosulfuron, resulting in reduced early yields. Dixie was the cultivar most tolerant to halosulfuron. Early flowering of Dixie was reduced 32–36% compared to 32–82% for the other cultivars. Marketable yield of summer squash was reduced 20–30% by all rates of halosulfuron when averaged over all application timings. Marketable yield of Seneca Prolific, Superpik, Dixie, Multipik, and Lemondrop was reduced 0–17% by halosulfuron PRE. Halosulfuron POST or PRE fb POST reduced marketable yield of all summer-squash cultivars by 25–46%. Thus, summer squash was not tolerant of POST halosulfuron; however, Dixie, Multipik, Seneca Prolific, and Superpik exhibited tolerance to halosulfuron PRE. Nomenclature: Halosulfuron; summer squash, Cucurbita pepo L. ‘Dixie’, ‘Multipik’, ‘Superpik’, ‘Seneca Prolific’ and ‘Lemondrop’. Additional index words: Sulfonylurea, vegetable tolerance to herbicides. Abbreviations: WAP, weeks after planting.

White Clover (Trifolium repens) Control and Flower Head Suppression in Apple Orchards

White clover is a weed in apple orchards that competes with the crop; also, flowers of this weed are unwanted attractants of honey bees at times when insecticides, which are harmful to these pollinators, are being applied. In 1997 and 1998, white clover flower head and plant control by clopyralid alone and with 2,4-D and apple tolerance to these herbicides were determined. Treatments consisted of clopyralid at 0.10 and 0.21 kg ae/ha, 2,4-D at 1.1 kg ae/ha, and 2,4-D at 1.1 kg ae/ha plus 0.03 or 0.05 kg ae/ha clopyralid, which were applied 2 wk before full apple bloom and 2 wk after full apple bloom, and a nontreated check. No crop injury occurred with any treatment. All herbicide treatments provided some white clover control and flower head suppression. No differences in white clover bloom reduction were observed through May among treatments containing clopyralid. As summer progressed, the effect of clopyralid rate became more apparent. Clopyralid at 0.21, regardless of application time, provided 99% vegetative control and 100% flower head reduction through July. Clopyralid plus 2,4-D controlled white clover better than 2,4-D alone. However, vegetative control and flower head reduction with clopyralid at reduced rates (0.03 or 0.05 kg ae/ha) plus 2,4-D were not acceptable (76% or less and 78% or less, respectively). Thus, clopyralid at 0.10 and 0.21 kg ae/ha will be necessary for acceptable white clover vegetation control and flower head reduction. Nomenclature: 2,4-D; clopyralid; white clover, Trifolium repens L. #3 TRFRE; apple, Malus domestica Borkh.; honey bees, Apis mellifera L. Additional index words: Orchard floor management, TRFRE, weed control. Abbreviations: 2WAFB, 2 wk after full apple bloom; 2WBFB, 2 wk before full apple bloom.

In-row Vegetation-free Strip Width Effect on Established ‘Navaho’ Blackberry

Abstract A field study was conducted in 2014 and 2015 in an established 5-yr old commercial blackberry planting to determine the effect of vegetation-free strip width (VFSW) on ‘Navaho’ blackberry vegetative growth, yield and fruit quality parameters, identify the optimum VFSW for blackberry plantings in the southeastern USA, and provide practical groundcover management recommendations that can increase the productivity of blackberry plantings. In Fall 2013, tall fescue was seeded in-row and allowed to establish. In Spring 2014, VFSW treatments (0, 0.6, 0.9, 1.2, and 1.8 m) were established in a randomized complete block statistical design with four replications. Blackberry growth measurements included primocane and floricane number, cane diam, individual fruit weight and yield. Fruit quality measurements included, soluble solids concentration (SSC), titratable acidity (TA) and pH. Primocane number increased with increasing VFSW in both years. Floricane number increased with increasing VFSW in 2014. Primocane diam decreased with increasing VFSW in 2014 but had a quadratic response in 2015. Berry weight and cumulative yield increased with increasing VFSW in both years. The only berry quality component affected by VFSW was pH, which decreased as VFSW increased. Results indicate that widening the VFSW in blackberry from the current recommendation of 1.2 m to 1.8 m could provide growers a means to increase plant growth, berry weight, and cumulative yield blackberry of a planting. Nomenclature: Blackberry, Rubus L.; tall fescue, Lolium arundinaceum (Shreb.) S.J. Darbyshire FESAR

Evaluating weed control and response of newly planted peach trees to herbicides

ABSTRACT Field experiments were conducted in North Carolina to determine peach response to herbicides. Mesotrione, rimsulfuron, and sulfentrazone did not injure newly planted peach trees. However, halosulfuron at the higher rate caused injury to peach trees, but did not reduce tree cross-sectional area or winter pruning weight. Another field experiment was conducted to determine the effect of herbicide-based programs on weed control. Sulfentrazone alone controlled common lamb’s-quarters and henbit but provided poor control of large crabgrass and yellow foxtail. However, a tank mix of norflurazon or oryzalin with sulfentrazone improved control of these weeds over sulfentrazone alone. Terbacil alone or in tank mix rimsulfuron, and flumioxazin alone gave excellent control of large crabgrass and yellow foxtail.

Vegetation-Free Strip Width Affects Growth, Berry Composition, and Yield of Cabernet franc in Vigorous Growing Environments

Summary Goals: In regions such as the eastern United States, excess vine vigor can be problematic. In this region, it is common to plant a perennial grass between rows, which can compete with vines for water and nutrients. The purpose of this research was to determine the effect of vegetation-free strip (VFS) width beneath the planted row on vine growth and fruit quality. The current recommendation for VFS width is 90 to 120 cm. However, modification of the VFS width can provide additional competition, limiting vine vigor. Determining the optimal width and effect of the VFS on vine size, berry composition, and yield would allow growers to optimize groundcover management in this region. Key Findings: Reducing VFS width decreased pruning weight/m cordon, shoot number/m cordon, lateral shoot number/cane, and summer fresh hedging weights. Narrowing the VFS width was most effective in the two of four years with the least rainfall. Yield/m cordon was reduced by narrowing VFS width, but not to below normal adjusted crop loads. Cluster weight, number of berries/cluster, and cluster number/m cordon were also reduced by narrowing VFS width. Berry soluble solids and total anthocyanins increased and TA decreased with decreasing VFS width, improving berry quality. Postveraison natural weed population growth in the VFS did not affect vine growth or fruit yield and composition. Impact and Significance: In the eastern United States, high rainfall and humidity promote excessive vine growth and immense pest pressure for Vitis vinifera production. Improved canopy characteristics could increase fruit quality by reducing pest pressure, by increasing soluble solids and total anthocyanin concentrations, and by improving the balance between pH and titratable acidity (TA). Increasing competition for water and nutrients during the growing season (by narrowing the VFS or allowing late-season weed competition) may be an effective way to accomplish these improvements. In this study, narrower VFS width in a tall fescue (Festuca arundinacea var. ‘Kentucky 31’) groundcover reduced vine vegetative growth and positively influenced berry composition. Vineyard weed populations that established naturally postveraison did not affect vine size, yield, or fruit quality.

Herbicide-Based Weed Management Programs in Erect, Thornless Blackberry

Field studies were conducted in 2009/2010 and 2011 in North Carolina to determine the influence of herbicide-based weed management programs on weed control and blackberry tolerance. Treatments consisted of five programs with a late fall-early winter herbicide application followed by (fb) an early spring herbicide application: flumioxazin fb flumioxazin, simazine fb terbacil, terbacil fb oryzalin plus simazine, norflurazon fb oryzalin plus simazine, and terbacil fb S-metolachlor plus simazine. A sixth program consisted of winter-applied dichlobenil. Crop tolerance and weed control were recorded at the physiological crop stages of budbreak, flowering, and harvest.