Carrier water quality is an important consideration for herbicide efficacy. Effect of carrier water pH (4, 6.5, or 9) and coapplied Zn or Mn foliar fertilizer was evaluated on glufosinate efficacy for horseweed and Palmer amaranth control in the field. Greenhouse studies were conducted to evaluate the effect of: (1) carrier water pH, foliar fertilizer (Zn, Mn, or without fertilizer), and ammonium sulfate (AMS) (at 0 or 2.5% v/v); and (2) carrier water hardness (0 to 1,000 mg L−1) and AMS (at 0 or 2.5% v/v) on glufosinate efficacy for giant ragweed, horseweed, and Palmer amaranth control. In a 2014 field study, control, plant density reduction, and biomass reduction were at least 8% greater for horseweed and at least 14% greater for Palmer amaranth when glufosinate was applied at carrier water pH 4 compared with pH 9. Glufosinate efficacy was at least 10 and 17% greater for giant ragweed and Palmer amaranth control, respectively, with carrier water pH 4 compared with pH 9 in the greenhouse. In the greenhouse studies, coapplied Zn or Mn fertilizer had no effect on glufosinate efficacy. Increased carrier water hardness from 0 to 1,000 mg L−1negatively influenced glufosinate efficacy and resulted in 20 and 17% lesser control and biomass reduction, respectively, on giant ragweed or Palmer amaranth. Use of AMS enhanced glufosinate efficacy on giant ragweed control in both greenhouse studies, whereas only the Palmer amaranth control was enhanced in the water hardness study. Horseweed control with glufosinate as affected by carrier water pH, hardness, or AMS remained unaffected in both greenhouse studies. Carrier water at alkaline pH or hardness > 200 mg L−1has potential to reduce glufosinate efficacy. Therefore, carrier water free of hardness cations and at acidic condition (pH = 4 to 6.5) should be considered for optimum glufosinate efficacy.

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Palmer amaranth (Amaranthus palmeriS. Watson) is a problematic weed encountered in U.S. cotton (Gossypium hirsutumL.) and soybean [Glycine max(L.) Merr.] production, with infestations spreading northward. This research investigated the influence of planting date (early, mid-, and late season) and population (AR, IN, MO, MS, NE, and TN) onA. palmerigrowth and reproduction at two locations. All populations planted early or midseason at Throckmorton Purdue Agricultural Center (TPAC) and Arkansas Agriculture Research and Extension Center (AAREC) measured 196 and 141 cm or more, respectively. Amaranthus palmeriheight did not exceed 168 and 134 cm when planted late season at TPAC and AAREC, respectively. Early season plantedA. palmerifrom NE grew to 50% of maximum height 8 to 13 d earlier than all other populations under TPAC conditions. In addition, the NE population planted early, mid-, and late season achieved 50% inflorescence emergence 5, 4, and 6 d earlier than all other populations, respectively. All populations established at TPAC produced fewer than 100,000 seeds plant−1. No population planted at TPAC and AAREC produced more than 740 and 1,520 g plant−1of biomass at 17 and 19 wk after planting, respectively. Planting date influenced the distribution of male and female plants at TPAC, but not at AAREC. Amaranthus palmerifrom IN and MS planted late season had male-to-female plant ratios of 1.3:1 and 1.7:1, respectively. Amaranthus palmeriintroduced to TPAC from NE can produce up to 7,500 seeds plant−1if emergence occurs in mid-July. An NEA. palmeripopulation exhibited biological characteristics allowing it to be highly competitive if introduced to TPAC due to a similar latitudinal range, but was least competitive when introduced to AAREC. AlthoughA. palmerioriginating from different locations can vary biologically, plants exhibited environmental plasticity and could complete their life cycle and contribute to spreading populations.

Most pesticide formulations such as dry flowables, emulsifiable concentrates and wettable powders are designed to be diluted with water as the carrier. A water pH higher than 7 which creates alkaline conditions can cause some pesticides to undergo degradation or chemical breakdown, a process known as hydrolysis. In general, insecticides are much more susceptible to hydrolysis than are fungicides, herbicides, defoliants or growth regulators. Organophosphate and carbamate insecticides are more susceptible than chlorinated hydrocarbon insecticides. Some pyrethroids exhibit susceptibility to hydrolysis.Tables reporting the pH of water sources across the U.S. list only a few states that have water with a pH below 7 which is in the acid range. The rest all have sources with varying degrees of alkalinity. Both surface and ground water supplies usually contain sufficient natural alkalinity to produce pH levels between 7 and 9.Some pesticides hydrolyze very rapidly. The hydrolysis rate can be rapid in the pH range of 8 to 9. For every pH point increase, the rate of hydrolysis will increase by approximately 10 times. The severity of losses due to alkaline hydrolysis is governed by the degree of water alkalinity, the susceptibility of the pesticide, the amount of time the pesticide is in contact with the water and the temperature of the mixture.The solution to the problem is lowering the pH of the water to the optimum range of 4 to 7 before mixing with the pesticide. This is accomplished by adding the recommended amount of buffering or acidifying agent. It should be noted that the buffering does not affect the residual activity of the pesticide. The buffering effect starts at the time of mixing, continues during storage in the tank, and does not stop until the water has evaporated from the spray droplet. Some materials, such as fixed copper fungicides including basic copper sulfate, copper oxide, and Bordeaux mixtures, should not be buffered as the acid solution may make the metals soluble and produce a phytotoxic effect when sprayed on plants. Products used to acidify tank solutions may be straight acidifying agents or in combination with surfactants or nutrient materials like trace elements or fertilizer products.A pH meter is the most accurate method of determining the pH of water. The use of test papers, such as litmus paper can be non-reliable and can be as much as two pH points in error. There air liquid color indicators (example: Bromothymol Blue) available which can indicate pH to within a half point. Water sources, both surface and ground, can and do change in pH with the passage of time. The change in pH is usually towards a more alkaline condition.

Substrate stratification is a method of filling nursery containers with “layers” of different substrates, or different textures of the same substrate. Recently, it has been proposed as a means to improve drainage, substrate moisture dynamics, and optimize nutrient use efficiency. Substrates layered with larger particle bark as the top portion and smaller particle bark as the bottom portion of the container profile would theoretically result in a substrate that dries quickly on the surface, thereby reducing weed germination, but that would also retain adequate moisture for crop growth. The objective of this study was to evaluate the effect of stratified substrates on the growth of common nursery weeds and ornamental crops. This study evaluated the use of coarser bark (<0.5 or 0.75 inches) as the top substrate and finer bark (<0.38 inches) as the bottom substrate with the goal of reducing the water-holding capacity in the top 2 to 3 inches of the substrate to reduce weed germination and growth. Results showed that substrate stratification with more coarse bark on the top decreased the growth of bittercress (Cardamine flexuosa) by 80% to 97%, whereas liverwort (Marchantia polymorpha) coverage was reduced by 95% to 99%. Substrate stratification initially reduced the growth of ligustrum (Ligustrum japonicum) and blue plumbago (Plumbago auriculata), but there was no difference in the shoot or root dry weights of either species in comparison with those of nonstratified industry standard substrates at the end of 24 weeks. The data suggest substrate stratification could be used as an effective weed management strategy for container nursery production.