Purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) tubers were stored at 5 C in soil treated at 0, 2, 3, 4, 6, 8, or 10 lb/A 2,6-dichlorobenzontrile (dichlobenil) for 2, 4, 6, 8, 10, or 12 weeks. Respiration of dormant tubers differed with species, unaffected by period of storage or dichlobenil concentration. Sprouting of untreated tubers decreased from 90% after 2 weeks storage to 43% after 12 weeks. Yellow nutsedge sprout production was uniform in time; purple nutsedge sprouting progressed to an 8-week high. Increased concentrations of dichlobenil progressively inhibited sprouting.

Overseeded rough bluegrass (Poa trivialis L. ‘Danish common’) and Italian ryegrass (Lolium multiflorum Lam. ‘Gulf’) maintained under putting green conditions were more susceptible to benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) and DCPA (dimethyl tetrachloroterephthalate) than creeping bentgrass (Agrostis palustris Hud. ‘Penn-cross’), red fescue (Festuca rubra L. ‘Dawson’), or perennial ryegrass (Lolium perenne L. ‘Medalist II’). February applications of 1.68 or 3.36 kg/ha of benefin and 6.72 or 13.44 kg/ha of DCPA caused significantly more discoloration and reductions in density than equivalent rates applied in March or April. Benefin was more injurious than DCPA to all overseeded species as judged by quality or density. DCPA caused significant delays in the breaking of dormancy of bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifdwarf’].

The use of nematodes as biological control agents has been met with skepticism, partly due to the newness of the approach and also to the potential difficulties of using a parasitic worm as a control organism. Most of the attention directed towards nematodes as biological control agents has been focused on several species that act as insect parasites. Considerable headway has been achieved with several of these parasites, especially with those parasitic on wood-boring insect larvae. The insect gallery of wood-boring larvae provides an optimum microclimate for the nematode to survive and seek out its larval insect host. A system where this strategy has proved successful involves the use of the insect parasitic nematode Neoaplectana carpocapsae Weiser as a biological control agent for carpenterworms (Prionoxystus robinae Peck) in fig (Ficus caria L.) orchards in California (6). Similar systems are being developed both here and abroad with the same nematode or a closely related genus or species. Many of these systems show promise (5).

Numerous investigations in which crop plants were utilized to study the effect, persistence, and movement of spray residues of 2,4–dichlorophenoxyacetic acid (2, 4–D) in a variety of soils and under a wide range of conditions have been reported. However, except for a report by Arle (1), a search of the literature has revealed no direct information on the effects of 2,4–D when applied in irrigation water to crop plants growing in the field. Arle treated cotton with irrigation water containing 2,4–D in equivalents ranging from 0.5 to 8 pounds per acre. Significant decreases in yield usually resulted from the higher rates of treatment when applications were made early in the season. Applications at the lower rates usually resulted in yields about equal to or greater than those obtained from check plots.

Sodium 2,2-dichloropropionate (dalapon) has been one of the more successful herbicides in controlling grass type weeds that have an abundance of underground rhizomes such as Johnsongrass (Sorgum halepense) and quackgrass (Agropyron repens).

Harvest weed seed control (HWSC) technology, such as impact mills that destroy weed seeds in seed-bearing chaff material during grain crop harvest, has been highly effective in Australian cropping systems. However, the impact mill has never been tested in soybeans [Glycine max (L.) Merr.] and weeds common to soybean production systems in the midwestern and mid-Atlantic United States. We conducted stationary testing of Harrington Seed Destructor (HSD) impact mill and winter burial studies during 2015 to 2016 and 2017 to 2018 to determine (1) the efficacy of the impact mill to target weed seeds of seven common weeds in midwestern and five in the mid-Atlantic United States, and (2) the fate of impact mill–processed weed seeds after winter burial. The impact mill was highly effective in destroying seeds of all the species tested, with 93.5% to 99.8% weed seed destruction in 2015 and 85.6% to 100% in 2017. The weak relationships (positive or negative) between seed size and seed destruction by impact mill and the high percentage of weed seed destruction by impact mill across all seed sizes indicate that the biological or practical effect of seed size is limited. The impact mill–processed weed seeds that retained at least 50% of their original size, labeled as potentially viable seed (PVS), were buried for 90 d overwinter to determine the fate of weed seeds after winter burial. At 90 d after burial, the impact mill–processed PVS were significantly less viable than unprocessed control seeds, indicating that impact mill processing physically damaged the PVS and promoted seed mortality overwinter. A very small fraction (<0.4%) of the total weed seed processed by the impact mill remained viable after winter burial. The results presented here demonstrate that the impact mill is highly effective in increasing seed mortality and could potentially be used as an HWSC tactic for weed management in this region.

In a series of seed burial studies, we tested the hypothesis that reduced tillage and cereal rye (Secale cereale L.) cover cropping influence seed persistence and that these effects are mediated by differences in fungal pathogens and exposure to light. Seeds of Powell amaranth (Amaranthus powellii S. Watson) and large crabgrass [Digitaria sanguinalis (L). Scop.] were buried in mesh bags in a long-term experiment with two levels of tillage (full-width tillage [FWT] or strip tillage [ST]) and two levels of cover cropping (none or cereal rye). In Experiment 1, seeds were exhumed each spring for 3 yr and tested for viability. In Experiment 2, untreated and fungicide-treated seeds were buried, exhumed at shorter intervals, and tested for viability. In addition, a subset of seeds in FWT treatments were exhumed and stored in either light or darkness during tillage operations and evaluated for persistence at 8.5 mo after burial (MAB). In Experiment 1, the persistence of D. sanguinalis seeds declined by 80% at 7 MAB regardless of cover crop or tillage treatment. The persistence of A. powellii seeds at 19 MAB declined by 95% in FWT compared with only 50% in ST. In Experiment 2, seed persistence of both species was greater in ST compared with FWT treatments, for seeds that had been exposed to light, but not for those that were maintained in darkness. Rye cover cropping resulted in a 2-fold increase in overwinter persistence of seeds of D. sanguinalis regardless of fungicide treatment. These results demonstrate that increased persistence under ST was primarily due to reductions in light-induced fatal germination and that increased overwinter persistence of D. sanguinalis in rye cover crop treatments could not be explained by differences in decay due to fungal pathogens controlled by the seed treatment.

The toxic effects of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to barley were avoided by feeding plants treated with 1.5 lb/A of simazine, sucrose, glucose, aspartate, and maltose. Shoots from plants fed glucose and maltose contained more soluble carbohydrate than the check. Plants fed glutamine and asparagine were higher in total nitrogen content than the check. Plants fed sucrose and maltose increased their nitrogen content over the check, but plants fed glucose did not. The harmful effects of simazine occurred primarily in barley shoots exposed to light. Plants grown in the dark showed a very small decrease in weight of shoots and soluble carbohydrate content as the level of simazine increased, while the weight of the shoots and soluble carbohydrate content of treated plants grown in the light decreased sharply. Simazine had little effect on root growth of plants grown in the light or dark. The data on root respiration showed that barley roots metabolized the added substances differently and that simazine differentially influenced their metabolism by the roots.

Two lines of corn (Zea mays L.)—one, GT112 RfRf, resistant to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and the other, GT112, susceptible to both—were used. Both glucose and sucrose, supplied to the treated plant through a severed leaf tip, were found to protect GT112 from the toxic effect of atrazine and simazine. Glucose gave a slightly better protection. Oxygen uptake in excised roots of GT112 treated with atrazine gradually declined with age until death, while leaf discs of treated and untreated lines showed no distinct trend in oxygen uptake. Atrazine decreased root respiration in GT112 but had no effect on that of GT112 RfRf. Root respiration in untreated GT112 was higher than in untreated GT112 RfRf. Atrazine decreased leaf respiration when both lines were considered.

The parasitic plant purple witchweed [Striga hermonthica (Delile) Benth.] poses a serious threat to cereal production in sub-Saharan Africa. Under natural infestation, the wild pearl millet [Pennisetum glaucum (L.) R. Br.] line 29Aw demonstrates resistance against the parasite, but the mechanism of its resistance is unknown. Striga resistance can be due to: (1) low induction of Striga germination (pre-attachment resistance) or (2) inhibition of parasite attachment and development (post-attachment resistance). Germination bioassays and root chamber (rhizotron) resistance-screening assays were used to determine the extent of pre- and post-attachment Striga resistance in 29Aw compared with the Striga-susceptible ‘SOSAT-C88-P10’ variety. Regarding pre-attachment resistance, 29Aw stimulated 10-fold less Striga seed germination at a maximum germination distance of 7.96 ± 2.75 mm from the host root compared with 35.94 ± 2.88 mm in SOSAT-C88-P10. Post-attachment resistance revealed 10- to 19-fold fewer and 2.5-fold shorter Striga seedlings with 28-fold less biomass growing on 29Aw compared with SOSAT-C88-P10. Microscopic analysis showed that Striga penetration in 29Aw was blocked at the endodermal and cortical levels. Post-attachment resistance in 29Aw was further supported by fewer (22%) Striga–host vascular connections in 29Aw compared with 79% in SOSAT-C88-P10. Together, these findings demonstrate that 29Aw harbors both pre- and post-attachment resistance mechanisms against S. hermonthica.

The evolution of herbicide-resistant weeds is a major concern in the corn- and soybean-producing Pampas region of Argentina, where growers predominantly plant glyphosate-resistant crop varieties and depend heavily on glyphosate for weed control. Currently, 16 weed species in Argentina are resistant to one or more of three different herbicide mechanisms of action, and resistant weed populations continue to increase, posing a serious threat to agricultural production. Implementation of integrated weed management to address herbicide resistance faces significant barriers in Argentina, especially current land ownership and rental patterns in the Pampas. More than 60% of Pampas cropland is rented to tenants for periods that rarely exceed 1 yr, resulting in crop rotation being largely abandoned, and crop export taxes and quotas have further discouraged wheat and corn production in favor of continuous soybean production. In this paper we discuss ways to facilitate new approaches to weed management in Argentina, including legal and economic reforms and the formation of a national committee of stakeholders from public and private agricultural sectors.

The herbicide l-(2-methylcyclohexyl)-3-phenylurea (siduron) suppressed the growth of soil bacteria, Azotobacter sp. and Chlorella vulgaris whereas siduron had no effect on actinomycetes, filamentous fungi, soil ciliates and other algae. Siduron had no effect upon the growth of Thiobacillus thioparus, Euglena gracilis, and Streptomyces griseus. The degradation product, 2-methylcyclohexylamine (hereinafter referred to as 2-MCHA) suppressed the growth of Aztobacter chroococcum and soil ciliates. Aniline, another degradation product of siduron, depressed the growth of Aspergillus versicolor and A. fischeri; however, A. ochraceus, A. candidus, A. clavatus, A. nidulans, A. flavus, Botrytis cinerea, and Rhizopus nigricans were not affected. None of these fungi was influenced in growth by 2-MCHA. Streptomyces griseus grew significantly less in the presence of aniline. The growth of Chlamydomonas pyrenoidosa, C. radiata, Anabaena catenula, and Rhizobium leguminosarum were not influenced by 10 ppm aniline or 10 ppm 2-MCHA.

In greenhouse and growth-chamber studies, increasing the level of either light or temperature increased bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] phytotoxicity to cucumber (Cucumis sativus L.). Light had a greater influence on phytotoxicity than did temperature. Light and temperature conditions after bentazon application had a greater influence on phytotoxicity than did light and temperature conditions before application. Maximum phytotoxicity was obtained from treatment with low light level before application and high light level after application.

Chlorsulfuron {2-chloro-N-[[(4-methoxy–6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} uptake from different pH solutions by leaves and excised root segments of velvetleaf (Abutilon theophrasti Medik. # ABUTH) was examined. In buffer solutions more 14C-chlorsulfuron penetrated intact leaves at lower pH levels (2.4, 3.4, and 4.4) than at pH 5.6. Initial chlorsulfuron absorption by 1-cm segments cut from the apical 5 cm of roots was rapid in the first 10 min for all pH levels. During the first 10 min, roots absorbed more chlorsulfuron from acidic (pH 2.4 and 3.4) than from higher pH solutions (pH 4.4 and 5.6). Chlorsulfuron efflux occurred in two phases for all pH levels. The first phase was a rapid loss through approximately 10 min, and the second a slow loss through 240 min. In the first 10 min, the efflux of chlorsulfuron was faster from roots incubated in pH 2.4 than in higher pH solutions. Efflux from the other pH levels was similar.

Multiherbicide granules were formulated containing 1.3% fluazifop {(±)-butyl 2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} (w/w) in polymerized tung oil overlaid on a granular matrix of gum xanthan-loess containing 2.7% linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide). Under greenhouse conditions the granules were as effective in selective control of velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), hemp sesbania [Sesbania exaltata (Raf.) Cory ♯ SEBEX], corn (Zea mays L. ♯ ZEAMX), and red rice (Oryza sativa L. ♯ ORYSA) in soybeans [Glycine max (L.) Merr. ‘Hill’] as when the herbicides were sprayed separately. When applied preemergence at 0.56 to 0.14 kg ai/ha, tung oil-encapsulated fluazifop on loess granules killed 100% of stolon bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] and was as effective as sprayed fluazifop.

White light-grown seedlings of smallseed dodder were cyclically irradiated from above with red light for 4 h followed by red plus far-red for 4 h. Tracings of initially nearly vertical, white light-grown seedlings were made from time-lapsed video images after four cycles of red light followed by red plus far-red. Stems of seedlings cycled into red light were negatively gravitropic and stems of seedlings then cycled into red plus far-red became photoreversibly, positively gravitropic. Observations suggest gravitropic sign reversal in smallseed dodder is regulated by photochrome.

Scanning electron microscopy (SEM) was used to study alachlor microcapsule morphology and the effects of straw age and moisture on herbicide release. Microcapsule diameter in the formulation ranged from 2 to 15 μm. The polyurea encapsulating material was stable in water over time. Diffusion was suggested as the primary mode of alachlor release, with diffusion rate controlled by herbicide and salt concentration gradients between the microcapsule and the surrounding aqueous solution. Alachlor release was promoted by drying the microcapsules before addition to water. Microcapsule morphology was unchanged 48 h after application to dry straw, and microcapsules did not appear to adhere to the straw surface. Microcapsules applied to overwintered wet straw were shriveled at 48 h after treatment, indicating herbicide loss. Capsule walls were broken and appeared brittle after application to fresh wet straw. Organic constituents of the fresh straw cuticle may affect capsule wall integrity.

In field and greenhouse studies, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was found to antagonize buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} injury to corn (Zea mays L.) when both herbicides were preplant incorporated. Similar results were found with five of seven other acetanilide herbicides tested. The antagonism between buthidazole and alachlor also occurred with common cocklebur (Xanthium pensylvanicum Wallr.) and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.] but not with five other weed species. Preplant-incorporated applications of alachlor had little to no effect on the response of corn to postemergence applications of buthidazole, but alachlor increased the susceptibility of ivyleaf morningglory to postemergence applications of buthidazole. No antagonism was observed when alachlor was included in postemergence applications of buthidazole to corn or ivyleaf morningglory.

Tolerance of strawberry to Colletotrichum gloeosporioides f. sp. malvae, (C. g. malvae) a mycoherbicide for control of round-leaved mallow, was tested in the growth chamber and field in an area infested with round-leaved mallow. No visual infections of C. g. malvae were observed on inoculated strawberry plants in the growth chamber or field. However, C. g. malvae was reisolated from inoculated leaves and petioles from both situations, but no adverse effects were observed on strawberry plant development in the growth chamber or on berry yield in the field. Round-leaved mallow competition was detrimental to strawberry establishment, and berry yield was reduced by half compared to weed-free plots. In round-leaved mallow infested plots, treatment with C. g. malvae resulted in more vigorous strawberry plants, with berry production almost to the level of weed-free. Therefore, use of this mycoherbicide for control of round-leaved mallow in strawberries is a viable option that fits well in an integrated pest management system.

The relationship between pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] in soil solution and dosage was examined in two soils under slurry equilibrium conditions and at field water capacity. In a sandy soil, the partition coefficient, calculated from a regression analysis of soil water content on dosage applied, was similar under slurry conditions and at field water capacity, but in a loamy sand, high in organic matter, the partition coefficient was somewhat higher at field water capacity than the estimated 4.71 measured in a great excess of water. In the sandy soil, neither the partition coefficients under slurry conditions nor at field water capacity were significantly different from Freundlich's k. Under slurry conditions in the loamy sand this difference was barely significant, whereas at field water capacity the estimated partition coefficient was significantly higher than Freundlich's k. Soil water sampling at field water capacity a fortnight after the start of the experiment showed a considerable increase in partition coefficient compared with the first sampling after 2 days, and the relationship in a sandy soil showed a slight non-linear trend, but that of the loamy sand still appeared to be linear. A desorption experiment indicated that the recovery of soil-adsorbed pyrazon was almost complete.