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  • Author or Editor: Rufus Isaacs x
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The increasing intensity and frequency of extreme heat events threaten crop productivity globally. Certain phases of plant reproduction necessary for fertilization are highly sensitive to extreme heat, particularly during pollen development, germination, and tube elongation. However, few studies have assessed the effects of extreme heat on pollen performance in perennial crop plants. To understand how northern highbush blueberry pollen responds to high temperatures, we quantified pollen germination and pollen tube growth in vitro using four commercially relevant cultivars (Bluecrop, Elliott, Jersey, and Liberty) in climate-controlled chambers. We also tested recovery from high heat in ‘Bluecrop’ to determine whether pollen tubes can still germinate and grow after short bursts of extreme heat. We found the highest proportion of germinated pollen tetrads and the greatest pollen tube growth at 20 and 30 °C, and the lowest levels at 10 and 40 °C, with nearly complete inhibition at 40 °C. Exposure to between 30 and 40 °C revealed significant reduction in pollen germination and tube growth above 35 °C across all cultivars and assessment times. Exposure to 37.5 °C for only 4 hours resulted in substantial reductions in pollen germination and pollen tube growth, even after pollen was moved to optimal conditions of 25 °C. Extreme heat exposure, even for a short duration, significantly limits blueberry pollen germination and tube development. This is expected to have cascading effects on fruit set and crop yield. The nonreversibility of the effects on pollen highlights the need to prevent fields reaching damaging temperatures by developing crop monitoring and management strategies to protect crops during bloom.

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Michigan higbush blueberry (Vaccinium corymbosum) growers were surveyed during Winter 2003 to gather information on the extent of the pest status of japanese beetle (Popillia japonica, Coleoptera: Scarabaeidae) within this crop, and their responses to this pest management challenge. The survey was mailed to 215 highbush blueberry farms in southwestern, central, and southeastern Michigan. Ninety-nine surveys were completed and returned. Our results revealed that this pest was of concern to the majority of growers who returned the survey (84%), causing average additional costs of $72/acre. Increased insecticide use was the major cause of the economic loss due to this pest, and the main methods for controlling japanese beetle were insecticides and clean cultivation. More farms had permanent sod coverage than clean cultivation in individual fields. The acreage of clean-cultivated farms was higher because larger farms tend to have clean cultivation. Japanese beetle has driven changes in row-middle management, indicated by growers who have switched to clean cultivation recently. Fifty percent of growers considered the changes they implemented to control japanese beetle to be effective, and most growers were not planning any further changes to their pest management programs to address this pest. Many growers were willing to try new cover crops if they are shown to be effective against japanese beetle.

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To maximize yield of pollination-dependent agricultural crops, farmers must ensure that sufficient pollinators are present when flowers are open and viable. We characterized and compared the lower development threshold temperature, bloom phenology, and flower viability of five common cultivars of highbush blueberry (Vaccinium corymbosum L.) to enable prediction of when flowers would be available for pollination. Threshold temperatures of all cultivars were found to be very similar and range between 7 and 8 °C. Logistic regression was used to characterize bloom phenology for all cultivars under field and greenhouse conditions. Bloom phenology under greenhouse conditions was delayed ≈100 growing degree-days when compared with field conditions. Average flower viability was determined daily from first flower opening until 5 days after flower opening for each cultivar. Results indicated declining flower viability with increasing flower age with most flowers unsuitable for pollination more than 4 days after opening. Implications of these results for planning pollination of highbush blueberry fields are discussed.

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The goal of this study was to evaluate potential alternatives to endosulfan for control of the blueberry bud mite (Acalitus vaccinii), because the availability of this acaricide may be restricted in the future. Laboratory evaluations of potential acaricides showed that endosulfan and a combination of abamectin plus oil provided 97% and 100% control, respectively. Pyridaben and fenpropathrin were less effective, reducing mite survival by 49% and 57%, respectively. Further laboratory evaluation of the abamectin plus oil treatment showed that each component applied alone provided a high level of control of blueberry bud mite. Field trials in Michigan on a mature highbush blueberry (Vaccinium corymbosum) planting were conducted to compare control of this pest by postharvest applications of endosulfan, delayed-dormant application of oil, or a combination of both treatments. The oil provided a 40% reduction in mite scores, while endosulfan was more effective (48%) and similar to the combination of endosulfan and oil (52%). A separate field trial using a multifan/nozzle sprayer that applied the pesticide in 233.8 L·ha-1 (25 gal/acre) of water suggested that the level of control from one application of endosulfan was not as effective as two applications. Results are discussed in relation to developing future bud mite control programs in blueberry and the need to address gaps in our understanding of the biology of blueberry bud mite. Endosulfan (Thiodan 50 WP), Endosulfan (Thiodan 3 EC), Abamectin (AgriMek 0.15 EC), Fenpropathrin (Danitol 2.4 EC), Pyridaben (Pyramite 60 WP).

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Seven primocane-fruiting and 15 floricane-fruiting raspberry varieties (Rubus idaeus) were compared for three fruiting seasons on a loamy sand soil in southwest Michigan. The earliest primocane-fruiting varieties (`Autumn Bliss', `Autumn Britten', `Polana') began ripening 3 weeks before the standard variety, `Heritage'. `Autumn Bliss' was the most productive early primocane-fruiting variety. `Caroline' and `Dinkum' ripened about 1 week earlier than `Heritage', and `Ruby' was 2 days later. `Caroline' was the most productive of this group and also had large fruit that were somewhat resistant to rot caused by Botrytis cinerea. `Caroline' also received the greatest leaf feeding from rosechafer beetles (Macrodactylus subspinosus). Most primocane-fruiting varieties were fairly resistant to leaf spot (Sphaerulina rubi), while `Dinkum' was highly susceptible to spur blight (Didymella applanata). Floricane-fruiting varieties were evaluated based on fruit production and quality as well as winter injury to canes, disease resistance, and feeding injury from two-spotted spider mites (Tetranychus urticae). The floricane-fruiting varieties showing minimal winter injury were `Boyne', `Killarney', `Latham', `Nova', and `Prelude'. `Canby', `Encore', `Glen Ample,', `Qualicum', `Reveille', `Titan', and `K 81-6' were moderately hardy; while `Tulameen', `Malahat', and `Lauren' were not hardy enough for this location. `Reveille', `Killarney', `Boyne', and `Prelude' were the most productive floricane-fruiting varieties. `Nova' and `Qualicum' had low levels of botrytis rot. `Nova' was most resistant to leaf spot and also had resistance to spur blight. Injury from mites was greatest on `Glen Ample' and lowest on `Malahat', `Prelude', `Qualicum', and `Tulameen'. `Caroline' (primocane-fruiting), `Prelude', and `Nova' (floricane-fruiting) were promising newer varieties.

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