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Abstract
The term allelopathy was introduced by Molisch (22) in 1937, and refers to all biochemical interactions (stimulatory and inhibitory) among plants, including microorganisms. The fact that the term is literally translated as “mutual harm or suffering” has probably led to other interpretations and confusion. Several scientists have suggested narrowing the definition to include only higher plants and harmful interactions. Rice (38) defined allelopathy in his first edition to include only harmful effects, but he recently opted to restate Molisch's premise in his 2nd edition (39). Molisch's broad definition of allelopathy is probably appropriate because considerable research has indicated that involvement of microorganisms and lower plants in phytotoxin production. Also, natural compounds that inhibit growth at certain concentrations often enhance growth at lower concentrations.
Abstract
Asparagus (Asparagus officinalis L. Cv. Cal. 711) grown both from seed and 1-year old crowns was maintained in a zero-tillage cultural system for 4 years and compared with that grown in a conventional tillage system. In the first 3 harvest seasons, yields of asparagus produced from crowns were increased 27% in the zero-tillage system. Asparagus from seed yielded as much as that from crowns after the third year, but spear size was appreciably smaller. Paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) in combination with either simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), monuron (3-(P-chlorophenyl)-1,1-dimethylurea), or terbacil (3-tert-butyl-5-chloro-6-methyluracil) provided excellent weed control during each growing season without injuring asparagus. Rotary chopping was a satisfactory method for returning mature brush to the soil. Additional advantages of zero-tillage were a reduction in volunteer asparagus seedlings, improved late season weed control, and less mechanical injury to crowns and buds. This cultural system provided excellent weed control in fields produced by direct seeding where crown depth was shallow and tillage impractical.
Abstract
Tank mixes of chloroxuron, fluazifop-butyl, and a crop oil concentrate were compared to single applications for annual weed control and safety on strawberries (Fragaria × ananassa Duch.). No noticeable synergistic or antagonistic effect on weed control was observed for mixtures of 4.48 kg·ha–1 chloroxuron and up to 0.14 kg·ha–1 fluazifop-butyl; injury to ‘Guardian’ strawberries was minimal. Early season daughter plant production and percentage of daughter plants rooted of ‘Honeoye’ strawberries was reduced by tank-mixing chloroxuron, fluazifop-butyl, and crop oil, and to a similar extent, from a mixture of chloroxuron and crop oil concentrate only. Chemical names used: N’-[4-(4-chlorophenoxy)phenyl]-N,N-dimethylurea (chloroxuron); (±)-butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid (fluazifop-butyl).
Abstract
Various fall-planted cover crops were evaluated for their influence on weeds and yield of ‘Midway’ and ‘Guardian’ strawberries (Fragaria x ananassa Duch). Rye (Secale cereale L. ‘Wheeler’) and wheat (Triticum aestivum L. ‘Yorkstar’) provided greater early season weed suppression than barley (Hordeum vulgare L. ‘Barsoy’). A high cover crop seeding rate increased weed suppression. Fruit yields were not reduced significantly by any of the cover crops.
Abstract
Testa of cucumber (Cucumis sativus L. PI 169391) seed contain inhibitor(s) that suppressed germination of proso millet (Panicum miliaceum L.) and seedling growth of cucumber. Seed fermentation and/or leaching with distilled water reduced inhibition, while activated charcoal eliminated the toxicity. Inhibitory effects of cucumber seed extracts on cucumber and proso millet germination decreased with maturity of the cucumber seed and fruit. PI 169391 seeds were both autotoxic and allelopathic during early seedling development. Partitioning with organic solvents demonstrated that the toxic compound(s) were polar. Extracts of other seed tissues were non-toxic as were extracts from seed and fruit of ‘Pioneer’ cucumber. Fruit juice extracts from PI 169391 suppressed growth of both cucumber and proso millet.
Abstract
Preplant-incorporated and post-transplant applications of napropamide [2-(α-naphthoxyl)-N, N-diethylpropionamide] were compared with 2 standard preemergent herbicides for safety on newly transplanted ‘Midway’ stawberries (Fragaria X ananassa Duch). Napropamide at rates up to 4.4 kg/ha caused no reduction in stolon or daughter plant production, or in rooting of daughter plants in the first season of growth. There was no adverse effect on fruit yield the following season when compared to hand-weeded controls. The plants responded similarly to the 2 application methods, except that slightly higher yields were obtained when all herbicides were preplant-incorporated.
Abstract
Nine herbicides were evaluated for their efficacy and safety in new plantings of pachysandra, English ivy, myrtle, and ajuga. Sprays of diphenamid, norea, simazine and trifluralin or granules of amiben and EPTC effectively controlled grasses and selected broadleaved weeds in two growing seasons. English ivy and pachysandra displayed excellent tolerance to all of the herbicides at the rates tested, although there was some injury observed from the 2× rate of simazine in 1969. Ajuga and myrtle exhibited a much wider range in susceptibility to the various herbicides. Preplant applications of trifluralin or post-transplant applications of norea gave good weed control and did not injure ajuga at two rates of application. Myrtle displayed adequate tolerance to both diphenamid and granular EPTC.
Abstract
Several annual and perennial weed species were effectively controlled with 3-tert-butyl-5-chloro-6-methyluracil (terbacil) in orchards. One-year-old seedling rootstocks of peach, Prunus persica, (L.) Patsch, were most tolerant to terbacil; pear, Pyrus communis, L., and apple, Malus sylvestris, L., seedlings were intermediate; the East Malling (EM) VII clone, Mazzard, Prunus avium, L., and Mahaleb cherry, Prunus mahaleb, L., seedlings were most susceptible. Both surface and soil incorporated applications were toxic, indicating that terbacil was readily leached into the root zone. Applications were made in 2 and 6-year-old experimental blocks and in commercial orchards (age 2–15 years) from 1965 to 1968. No major damage was observed on apple, peach, tart cherry or sweet cherry trees that were established 3 years or longer. Toxicity symptoms manifested as veinal chlorosis were occasionally observed on sandy loam soils at rates 2–3 fold greater than required for satisfactory weed control.
During Spring and Summer 1989 and 1990, the Maryland Dept. of Agriculture obtained several barrenwort (Epimedium sp. C. Morr. and Decne.) hybrids showing virus-like symptoms, including mosaic, line pattern, and concentric chlorotic ringspot. Viral-associated, double-stranded RNA analysis, electron microscopy, serology, and host reactions indicated the presence of a virus with properties similar to those of the tobamovirus group. Serologically, the virus was closely related to tomato mosaic virus. Attempts to infect barrenwort by mechanical inoculations were unsuccessful. This is the first report of a viral infection of barrenwort.