Populations of the waterhyacinth mite (Orthogalumna terebrantis Wallwork) of ca 200,000 galleries/m2 (or 10,000 per plant) caused serious damage to waterhyacinth [Eichhornia crassipes (Mart.) Solms.] in the field, but such damage was sporadic and confined to small areas of plants in midsummer. Two or three generations a year occurred in the field. Adults emerged in late December, March, and May and adults were found on waterlettuce (Pistia stratiotes L.) throughout the winter. Development, appearance of the different stages, behavior of immatures and adults, and manner of attacking waterhyacinth is described. Only small differences were found between the biology of the mites studied in Argentina and of that reported in Uruguay and the United States.

A rapid cotyledon disc bioassay developed for photosynthetic inhibitors was tested on several herbicides of different modes of action. In addition to being an excellent bioassay method for photosynthetic inhibitors it was found to be useful for the detection of diquat (6,7-dihydrodipyrido[1,2-α:2′,1′-c] pyrazine-diium ion), paraquat (1,1′-dimethyl-4,4′-dipyridinium ion), and dinoseb (2-sec-butyl-4,6-dinitrophenol). Herbicides representing several other modes of action could not be readily detected by this method.

In field studies, HOE 22870 [4-(4′-chlorophenoxy)-phenoxy-α-propionic-isobutylester] and HOE 23408 methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate at 0.84 to 3.36 kg/ha were sprayed over the top of soybeans [Glycine max (L.) Merr.], corn (Zea mays L.), and giant foxtail (Setaria faberi Herrm.). Rates of 0.84 or 1.68 kg/ha of either herbicide controlled corn and giant foxtail. Soybeans tolerated 3.36 kg/ha (the highest rate used) of either herbicide. Both herbicides performed quite similarly, but HOE 22870 was generally more effective on giant foxtail and less effective on corn than was HOE 23408. The optimum time of application, in terms of soybean development, was the first trifoliolate stage. At this stage, corn had four to five leaves and giant foxtail had three to five leaves. HOE 23408 was applied to 32 inbred lines of corn in a greenhouse study. Several inbreds had considerable tolerance. When HOE 23408 at 0.56 kg/ha was applied to these 32 inbreds in a field study, control ranged from 100% for the most susceptible inbred to 22% for the most resistant inbred. At 1.12 kg/ha, control of corn ranged from 100% to 42%.

Johnsongrass [Sorghum halepense (L.) Pers.] regrowth was used as an index for penetration and translocation of dalapon (2,2-dichloropropionic acid) with and without adjuvants under different environmental conditions. Johnsongrass control with dalapon at 1.12 kg/ha without surfactant decreased as air temperature increased from 16 to 27 to 38 C. Plants at 16 and 27 C with 100% relative humidity (RH) were more susceptible to dalapon without surfactant than were plants at 35% RH. The presence of 1% surfactant in dalapon solutions increased johnsongrass control above that of dalapon alone at 27 and 38 C regardless of RH. Adding 1% surfactant and maintaining plants at 100% RH and 38 C resulted in significantly less johnsongrass control than that at 35% RH and 38 C. The addition of 0.1 M KH2PO4 to mixtures of dalapon + surfactant restored effectiveness at 100% RH and 38 C. Dalapon applied without surfactant was more injurious to johnsongrass grown with 40% soil moisture than with 25% soil moisture regardless of air temperature or RH. When plants were maintained at 27 or 38 C with 25% soil moisture, 0.1 M KH2PO4 + surfactant was more beneficial than surfactant alone in increasing dalapon toxicity to johnsongrass. At 40% soil moisture, johnsongrass control with dalapon + 1 % surfactant was not improved with the addition of KH2PO4 regardless of air temperature.

Over a 3-yr period 10 herbicides were tested alone or in combination for control of weeds and for effects on growth of nursery stock in containers. Annual bluegrass (Poa annua L.) was controlled by norea [3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea], alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], and combinations of diphenamid (N,N-dimethyl-2,2-diphenylacetamid), trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] plus simazine [2-chloro-4,6-bis(ethylamino)-s-triazine]. Bittercress (Cardamine oligosperma Nutt.) was controlled by simazine, oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one], and norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone]. Mouseear chickweed (Cerastium vulgatum L.) was controlled by dichlobenil (2,6-dichlorobenzonitrile) and norflurazon, and common groundsel (Senecio vulgaris L.) was controlled by dichlobenil and norflurazon. Some of the treatments decreased growth of certain nursery cultivars.

In the greenhouse, postemergence treatments of 1.12 kg/ha of HOE 22870 [4-(4′-chlorophenoxy)-phenoxy-α-propionic-isobutylester] or HOE 23408 methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate were applied to three perennial weeds (two grasses and one sedge) and to 27 species or varieties of annual grasses (crops and weeds). The perennials were resistant to both compounds, but control of the seedling grasses ranged from 0 to 100%, indicating the potential of controlling certain grass weeds in certain grass crops, as well as in broadleaf crops. Generally, the response of a given species was similar for both compounds. However, on some grasses one compound was considerably more effective than the other. Seven species or varieties of foxtail (Setaria spp.) were treated with various rates of either compound. Differential responses were observed, but it appeared that all the foxtail species or varieties studied should probably be controllable with HOE 23408. All but yellow foxtail [Setaria lutescens (Weigel) Hubb.], should probably be controllable with HOE 22870.

The comparative morphological development of six johnsongrass [Sorghum halepense (L.) Pers.] ecotypes was studied over a 10-week period. Three of the ecotypes were previously shown to be susceptible to dalapon (2,2-dichloropropionic acid) while others were resistant to the herbicide. The production of primary culms varied from 5.0 to 9.3 per plant system, and secondary culms ranged from 7 to 24 per plant system. Plant heights varied nearly two-fold, and the number of individual rhizomes produced by different ecotypes varied three-fold. Susceptible ecotypes from Georgia, Washington, and Illinois produced more rhizome nodes and higher dry and wet weights of culms and rhizomes than resistant ecotypes from Mississippi, Louisiana, and California. Ecotypes most resistant to dalapon had longer rhizome internodes and higher water content in culms and rhizomes than susceptible strains. Differences in anatomy and growth support the hypothesis of the existence of johnsongrass ecotypes, but the results were not consistent with the susceptibility of ecotypes to dalapon.

Benthiocarb S-[(4-chlorophenyl) methyl] diethylcarboamothioate which was applied postemergence, altered the growth and development of shoots of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and bearded sprangletop [Leptochloa fascicularis (Lam.) Gray] seedlings, two gramineous annual weeds commonly found in rice fields. The herbicide did not affect root development of either species. Benthiocarb retarded the growth of new leaves within the extending leaves and caused swelling of cells. The cells of the shoot apices of treated seedlings were often vacuolated. Tubular-like leaves were induced by benthiocarb, but their formation differed from that caused by phenoxy herbicides.

The divisions and subjects of weed biology were identified. Twenty-eight representatives from the herbicide industry ranked the priority of the identified subjects. They also gave their thoughts and impressions on specific questions dealing with weed biology. The divisions which received a moderate to high priority rating are: Identification and Classification of Weeds, Harmful Aspects of Weeds, Weed Growth and Development, and Weed Control. A review of the papers published in Weed Science indicates an increase in the number of papers being published on the subject of weed biology and a decrease in the number of papers dealing with chemical control. The proceedings of the regional weed societies in the U.S.A. had a high percent of the papers devoted to chemical control, with the lowest percentage devoted to weed biology. Comments are made as to why weed biology is important and how research data on weed biology would be used by industry. A comparison of the rating that industry assigned to the various subjects of weed biology to the amount of published literature indicates insufficient work has been done in many areas. It also appears that there is an imbalance in research. More work is being done on certain subjects that industry considers of lesser value than subjects of greater importance.

Experiments involving the application of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 0.56, 1.12, or 1.68 kg/ha on each of three successive plantings of pickling cucumbers (Cucumis sativus L. ‘Explorer’) were conducted during a 2-yr period. Residues of nitralin in soil increased with rate and number of applications. Nitralin residues accumulated to higher concentrations in a soil with 2.9% organic matter than in a soil with 0.7% organic matter. However, cucumber plants were injured less in the soil with the highest concentrations of herbicide. Oats (Avena sativa L. ‘Carolee’) planted following cucumbers were injured by nitralin residues resulting from the highest application rates. Bioassays and chemical analyses suggested that no appreciable soil residues of nitralin remained during the succeeding year.

Six-week-old honey mesquite [Prosopis glandulosa (Torr.) var. glandulosa] seedlings were treated with various concentrations of ethephon (2-chloroethylphosphonic acid) and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] alone and in combinations to determine effect on stem mortality under greenhouse conditions. Ethephon alone at 0.05 g/L brought about defoliation and a reduction in xylem tissue formation but did not affect the histological development of the stem tissue. Treatment with 2,4,5-T alone at 3.2 g/L resulted in 40% stem mortality along with the formation of abnormal xylem tissue of reduced thickness. A combination of ethephon (0.05 g/L) and 2,4,5-T (3.2 g/L) significantly increased mesquite mortality. This was associated with a further reduction in xylem thickness, abnormal development of the xylem, abnormal positional relationships of vascular tissues, and initiation of adventitious roots. This study showed that ethephon in combination with 2,4,5-T was more effective than either treatment alone in promoting the disruption of the tissue systems of the stem and in increasing control of mesquite seedlings.

Maximum activity of isocitric lyase (EC 4.1.3.1) was reached at 24 hr incubation of afterripened (nondormant) prickly sida (Sida spinosa L.) seed. Enzyme activity declined gradually with incubation times in excess of 24 hr. Actinomycin D (Act D) at 5 μg/ml had essentially no effect on 24-hr germination but inhibited development of isocitric lyase activity 83%. Cycloheximide (CH) at 10 μg/ml inhibited 24-hr germination of punctured seed only 7% but inhibited development of isocitric lyase activity 76%. Seed incubated in water 12 hr before being transferred to Act D at 5 μg/ml for an additional 12 hr did not escape sensitivity to the antibiotic. Isocitric lyase activity was inhibited when assayed at 24 hr total incubation. In the reverse experiment, seed incubated in Act D 12 hr before being transferred to water, isocitric lyase activity at 24 hr was not affected. Apparently prickly sida seed lacked a performed mRNA for isocitric lyase and transcription and translation of the mRNA occurred shortly after initiation of radicle protrusion (~8 hr).

The tolerance of bermudagrasses ‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, ‘Ormond’, and ‘Floraturf’ [Cynodon dactylon (L.) Pers.] cultivars to repeated annual applications of oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] and butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] were evaluated over a 4-yr period. Oxadiazon treatments did not affect growth characteristics of these bermudagrasses. Butralin caused moderate to severe reduction in sod density. ‘Tifway’, ‘Ormond’, and ‘Floraturf’ were more tolerant to butralin than ‘Tifgreen’ and ‘Tifdwarf’.

Lateral roots of a clone of field bindweed (Convolvulus arvensis L.) were dug each month for 12 months, cut into 6-cm long sections and grown in the dark on moist paper at 23 C to determine if regeneration varies seasonally. New shoots and roots were measured after 8, 11, and 14 days. After 14 days, 69% to 98% of the sections had produced shoots. The mean number of shoots per section was greatest in April (6.4) and least in November (2.0). The monthly mean shoot length ranged from 24 to 43 mm. Although most sections produced shoots, very few produced roots. In May, 31% of the sections grew roots, but only 2% to 16% had new root growth in the other months. For the test period, 83% of the sections produced shoots and only 10% produced roots.

Field experiments were conducted for 2 yr on pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide] treatments in the Piedmont region of Georgia to aid the transition of overseeded cool-season turf to warm-season turf in early spring. Pronamide applied to overseeded perennial ryegrass (Lolium perenne L. ‘Game’ and ‘Manhattan’) gradually reduced the growth of perennial ryegrass and permitted bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifdwarf’] to initiate spring growth with little competition. Total turfgrass cover and turf quality ratings in pronamide treated plots were lower than ratings for untreated plots during the transition period. However, the reduction in turf quality and stand was minimal when pronamide was applied March 20 at 0.8 kg/ha. The turf quality and stand was 76 and 88% of the untreated check on April 23 and May 9, respectively, but the turf fully recovered within 2 weeks. The turf quality was higher in plots treated with pronamide on March 20 than in untreated check throughout June. The optimum date of promanide treatment in the Piedmont Region for transition of cool-season grass to warm-season grass was March 20, when compared to applications made on February 28, April 9, or April 29.

The dissipation of sodium azide (NaN3) from soil was significantly affected by pH, soil moisture, and relative humidity (RH). Loss was more rapid from acid than from alkaline soils. Moist soil (20 to 60% field capacity) or air dry soil in a moist environment (100% RH) lost NaN3 more rapidly than air dry soil in a dry (0% RH) environment. However, dissipation was decreased when soil moisture exceeded 60% field capacity. Degree of leaching and phytotoxicity of NaN3 was not affected by soil pH. Bioassay studies indicated that 10 ppm NaN3 in the soil significantly reduced germination and growth in plant species tested. At concentrations of NaN3 below 10 ppm, plant germination was often delayed but normal growth occurred after NaN3 dissipation.

Benzoylprop ethyl [Ethyl N-benzoyl-N (3,4-dichlorophenyl)-2-amino-propionate] and WL 29761 [methyl-N-benzoyl-N-(3-chloro-4-fluorophenyl)-2-amino-propionate] were applied to wild oat (Avena fatua L.) in wheat (Triticum aestivum L. ‘Manitou’) to study the yield benefits occurring and the efficacy of the compounds on wild oat. Even though removal of the wild oat was at the later growth stages, benzoylprop ethyl and WL 29761 did produce significant yield increases at both rates tested. Efficacy on wild oat ranged from mediocre to virtually complete control. Crop tolerance was satisfactory throughout the study.

Corn (Zea mays L.) was grown in EPTC-(S-ethyl dipropylthiocarbamate) and butylate-(S-ethyl diisobutylthiocarbamate) treated soil at 33 and 15% moisture in growth chambers at 30 and 20 C. EPTC (6 and 18 ppm) and butylate (19 and 50 ppm) reduced corn growth more at 30 than at 20 C. The days before emergence of the corn coleoptile were the most critical time for thiocarbamate injury. When plants were grown at 30 C before emergence more injury occurred at 33% soil moisture than at 15% except with butylate at 19 ppm. At 20 C, however, plants grew as tall or taller at 33% soil moisture than at 15% except for butylate at 19 ppm. Addition of R-25788 (N,N-diallyl-2,2-dichloroacetamide) to EPTC and butylate increased by about 10 times the amount of herbicide required to injure corn. With R-25788 the toxicity of these two herbicides was not influenced greatly by either temperature or soil moisture.

Five crops were grown for three seasons following a single soil-incorporated application of MSMA (monosodium methanearsonate). Crop sensitivity to soil arsenic decreased as follows: snap beans (Phaseolus vulgaris L. ‘Early Gallatin’ and ‘Tenderette’); rice (Oryza sativa L. ‘Dawn’ and ‘Starbonnet’); soybeans [Glycine max (L.) Merr. ‘Lee 68′]; potatoes (Solarium tuberosum L. ‘Red LaSoda’ and ‘Red Pontiac’); and cotton (Gossypium hirsutum L. ‘Stoneville 7A’). Over the 3-yr period, yield of snap beans was reduced 8, 14, and 85% below the untreated check where MSMA had been incorporated initially at 22, 45, and 269 kg/ha, respectively. Similar reductions in yield of rice were 18, 25, and 55%. Soybean and potato yields were significantly reduced only at the highest rate of MSMA while cotton yields were unaffected. Arsenic content in the edible portion of the crops decreased as follows: rice, snap beans, potatoes, soybeans, and cotton. The arsenic content in crops from the highest MSMA plots seldom exceeded twice that from the untreated plots.

The influence of several factors on the injury to corn (Zea mays L.) seedlings from high rates of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) was determined in growth chambers. This herbicide combination severely injured 6% of the corn seedlings at rates as low as 14 ppm if the herbicide was poorly incorporated into the soil. If thoroughly incorporated, severe injury did not occur unless the rate of application exceeded 56 ppm. Decreased injury resulted when seed were placed so as to insure rapid shoot emergence. Seed planted at 2 cm with its coleoptile pointed upward or horizontally (with posterior facing upward) was injured less than in other positions, Corn cultivars differ in their susceptibility to EPTC + R-25788 at 30 but not at 20 C. Of the several corn cultivars tested at 30 C, SX-98 was the least injured by EPTC + R-25788. Corn injury was progressively reduced as leaching volumes were increased and as the time from herbicide application to corn planting was increased.