The Invasive Weed Trianthema portulacastrum in Israel.

Trianthema portulacastrum L. (Aizoaceae), commonly known as desert horse purslane or black pigweed, is a C4 dicot succulent annual herb that is widespread in Southeast Asia, tropical America, Africa, and Australia. In Israel, it is an invasive weed of increasing importance in agricultural fields. The aim of this study was to investigate the biology of this invasive weed and its spread in the Hula Valley of Israel. Initial studies included the investigation of the T. portulacastrum specimens held at the Israel National Herbarium. On-site surveillance for the identification of weed infestation locations was conducted in the Hula Valley throughout 2019-2022, and an infestation map was assembled. In a study of the plant biology, greenhouse pot experiments revealed that T. portulacastrum seeds emerge best from the upper soil levels, and as seed depth increases, the emergence rate decreases, so that at 6 cm soil depth, there was no emergence. In controlled-environment growth chamber studies, there were no significant differences in germination with or without light. A maximum germination of 81% was observed for a 12 h night/day of 25/35 °C regime. Germination rates decreased with the decrease in temperature. A seed germination thermal time model that was developed for estimating the minimum temperature required for germination (Tbase) computed this temperature to be 10 °C. This study revealed the biology, in particular seed germination and emergence requirements, of the invasive weed T. portulacastrum that has spread in the Hula Valley in Israel and beyond. Future research will focus on an examination of control measures to combat this invasive weed.

"Parasitic Weeds: Biology and Control" Special Issue Editors Summary.

We are happy to summarize this important Special Issue (SI) of MDPI Plants-"Parasitic Weeds: Biology and Control" [...].

Imazapic Herbigation for Egyptian Broomrape (Phelipanche aegyptiaca) Control in Processing Tomatoes-Laboratory and Greenhouse Studies.

Parasitic plants belonging to the Orobanchaceae family include species that cause heavy damage to crops in Mediterranean climate regions. Phelipanche aegyptiaca is the most common of the Orobanchaceae species in Israel inflicting heavy damage to a wide range of broadleaf crops, including processing tomatoes. P. aegyptiaca is extremely difficult to control due to its minute and vast number of seeds and its underground association with host plant roots. The highly efficient attachment of the parasite haustoria into the host phloem and xylem enables the diversion of water, assimilates and minerals from the host into the parasite. Drip irrigation is the most common method of irrigation in processing tomatoes in Israel, but the delivery of herbicides via drip irrigation systems (herbigation) has not been thoroughly studied. The aim of these studies was to test, under laboratory and greenhouse conditions, the factors involved in the behavior of soil-herbigated imazapic, and the consequential influence of imazapic on P. aegyptiaca and tomato plants. Dose-response Petri dish studies showed that imazapic does not impede P. aegyptiaca seed germination and non-attached seedlings, even at the high rate of 5000 ppb. Imazapic applied to tomato roots inoculated with P. aegyptiaca seeds in a PE bag system revealed that the parasite is killed only after its attachment to the tomato roots, at concentrations as low as 2.5 ppb. Imazapic sorption curves and calculated Kd and Koc values indicated that the herbicide Kd is similar in all soils excluding a two-fold higher coefficient in the Gadash farm soil, while the Koc was similar in all soils except the Eden farm soil, in which it was more than twofold lower. In greenhouse studies, control of P. aegyptiaca was achieved at >2.5 ppb imazapic, but adequate control requires repeated applications due to the 7-day half-life (t1/2) of the herbicide in the soil. Tracking of imazapic in soil and tomato roots revealed that the herbicide accumulates in the tomato host plant roots, but its movement to newly formed roots is limited. The data obtained in the laboratory and greenhouse studies provide invaluable knowledge for devising field imazapic application strategies via drip irrigation systems for efficient and selective broomrape control.

Control of Egyptian Broomrape in Processing Tomato: A Summary of 20 Years of Research and Successful Implementation.

The obligate root parasitic weeds commonly known as broomrape (Orobanche and Phelipanche spp.) cause severe damage to vegetable and field crops worldwide. Efficient control of these parasites is difficult due to their development and attachment to the host plant (via a specialized organ, the haustorium) under the soil surface and to their unique biological traits of massive seed production, facile seed dispersal, germination only under specific conditions, and seed longevity. The major damage inflicted by the parasites takes place underground, making control extremely challenging. Egyptian broomrape (Phelipanche aegyptiaca) is a devastating pest in the Mediterranean basin, parasitizing a wide host crop range, including tomato, sunflower, legumes, and carrot, resulting in severe crop losses. Twenty years of research have led to the development of integrated smart management strategies for combating this parasite in processing tomato fields. In particular, an explicit decision support system (DSS) designated PICKIT has been developed; this DSS is based on predicting parasitism dynamics and employing a range of selective targeted chemical applications (preplanting incorporation, foliar application, and herbigation). In this feature article, we describe the evolution of this research from the laboratory, through greenhouse and experimental field trials, to large scale commercial fields and the successful assimilation of PICKIT into agricultural practice. The use of PICKIT in fields of processing tomatoes in northern Israel has led to effective control of Egyptian broomrape, even in fields with high infestation levels, resulting in a tomato yield increase of an average of 40 tons ha-1 compared with nontreated plots. In 2016, PICKIT was commercially implemented in 33 fields, totaling 400 ha, giving 95% Egyptian broomrape control and tomato yields of 115 to 145 tons ha-1. The outcome of this research is now enabling farmers to grow tomatoes in Egyptian broomrape-infested fields with assured increased yields and hence high profits.

Development and employment of slow-release pendimethalin formulations for the reduction of root penetration into subsurface drippers.

Subsurface drip irrigation supplies water directly to the root zone and is an efficient irrigation technology. One of the main challenges is preventing plant roots from clogging the drippers. With the aim of inhibiting root penetration, slow-release pendimethalin formulations based on its solubilization in micelles adsorbed and unadsorbed to clay were developed. In the past unadsorbed micelles were considered inadequate for slow release, because release was too fast. In contrast, the advantage of a two-mode release formulation, composed of adsorbed and unadsorbed micelles, is demonstrated. A bioassay to study pendimethalin leaching at a refined scale of 1-2 cm was developed and reduced leaching from the micelle-clay formulations in comparison to the commercial formulation (Stomp) was exhibited. In a greenhouse study the application of the formulations by injection into an irrigation system was extremely efficient with 0-10% root penetration in comparison to 100% penetration upon Stomp injection.

Effect of soil wetting and drying cycles on metolachlor fate in soil applied as a commercial or controlled-release formulation.

A controlled-release formulation (CRF) has been developed for metolachlor, which reduced its leaching in a sandy soil and improved weed control in comparison with the commercial formulation. The current study tested the effect of soil wetting and drying cycles (WDCs) on metolachlor fate (desorption, leaching, and weed control) applied as the CRF and as the commercial formulation. Metolachlor adsorption to a heavy soil (Terra-Rosa) was predominately to the clay minerals and oxides. Metolachlor release from a heavy soil subjected to WDCs was higher than its release from the soil not subjected to WDCs. Consequently, a bioassay in soil columns treated with the commercial formulation indicated enhanced metolachlor leaching in heavy soils under WDCs. In contrast, when metolachlor was applied as the CRF, leaching was suppressed and not affected by WDCs. These results emphasize the advantages of the CRF also in heavy soils subjected to WDCs.

Resistance of red clover (Trifolium pratense) to the root parasitic plant Orobanche minor is activated by salicylate but not by jasmonate.

BACKGROUND AND AIMS: Obligate root holoparasites of the genus Orobanche attack dicotyledonous crops and cause severe losses in many parts of the world. Chemical induction of plant defence systems such as systemic acquired resistance was proposed to be an available strategy to control the root parasite, but the detailed mechanisms involved have not been clarified. The aim of this study was to elucidate the effects of salicylic acid (SA), jasmonic acid (JA) and their analogues on resistance of red clover to Orobanche parasitism. METHODS: Roots of red clover grown in plastic chambers were applied with SA, S-methyl benzo[1,2,3]thiadiazole-7-carbothioate (BTH), methyl jasmonate (MeJA) and n-propyl dihydrojasmonate (PDJ), and then were inoculated with O. minor seeds. Attachments of the parasite were observed after 5 weeks. KEY RESULTS: SA and BTH, inducers of SA-mediated defences, significantly reduced the number of established parasites by more than 75 %. By contrast, MeJA and PDJ, inducers of JA-mediated defences, did not affect parasitism. The reduction in the number of established parasites by SA and BTH was due to the inhibited elongation of O. minor radicles and the activation of defence responses in the host root including lignification of the endodermis. CONCLUSIONS: These results suggest that SA-induced resistance, but not JA-induced resistance, is effective in inhibiting Orobanche parasitism and that the resistance is expressed by the host root both externally and internally.