The genus Physalis belongs to the family Solanaceae and includes 100 known species of annual and perennial plants, of which three are grown as vegetables: Physalis ixocarpa Brot. ex Horm., Physalis peruviana L. and Physalis pruinosa L. (Abak, Guller, Sari, & Paksoy, 1994; Legge,1974; Santiaguillo-Hernández, Cedillo-Portugal, & Cuevas-Sánchez, 2010).
The husk tomato (P. ixocarpa), also called green tomato or tomatillo, is native to Mexico and was domesticated by the Mesoamerican peoples. It is currently distributed throughout Mexico, although the greatest genetic diversity is concentrated in the western center of the country (Santiaguillo-Hernández et al., 2010). It grows both in the wild and in traditional polyculture production systems, so it is still possible to find it as a weed, either encouraged or tolerated (Santiaguillo-Hernández et al., 2012). Despite the widespread use of herbicides in market agriculture, wild husk tomatoes often grow amid crops such as corn (Zea mays L.) and sorghum (Sorghum bicolor [L.] Moench), especially in central western Mexico, where their collection is common and of high value for farmers (Peña-Lomelí, & Márquez-Sánchez, 1990; Santiaguillo-Hernández et al., 2012).
Husk tomatoes are widely grown in Mexico for food use and are produced in almost the entire country. It is grown in both irrigated and rainfed systems in the autumn-winter and spring-summer cycles. The state with the largest harvested area and production volume is Jalisco, followed by Nayarit, Sinaloa, State of Mexico, Puebla and Michoacán. In 2015, this crop ranked seventh in area planted with vegetables, with a national average yield of 14.682 t·ha-1 (Servicio de Información Agroalimentaria y Pesquera [SIAP], 2015), which is considered low in relation to the crop’s productive potential, estimated at 40 t·ha-1 (Peña-Lomelí, Santiaguillo-Hernández, & Magaña-Lira, 2007; Peña-Lomelí, Ponce-Valerio, Sánchez-del Castillo, & Magaña-Lira, 2014).
The cultivation of husk tomatoes can be established both by direct sowing and by transplanting and, in general, weed control is carried out mechanically and manually, combining mechanized farming with weeding by hand or hoeing. In both irrigated and rainfed systems, it is common for two or three weedings to be carried out, which implies a cost of 30 or more days’ wages per hectare, representing up to 25 % of the crop’s production costs. Timely weed control is essential to obtain a good yield, and is critical when the crop is established by direct sowing, as the tomato emerges at the same time as the weed. In this context, it is necessary to keep the crop free of weeds in the critical period of competition, 40 days after transplant (dat) or 60 days after direct sowing (Roque, Pedro, & Peña-Lomelí, 1995).
Despite the horticultural importance of the crop and the high cost of weed control, little research has been done on the use of herbicides, although some are reported as selective for the species. Roque et al. (1995) evaluated eight herbicides in husk tomato crops, both in direct sowing and in transplant, and observed that the herbicides Trifluralin (1.5 L·ha-1), Napropamide (5 L·ha-1) and Bensulide (10 L·ha-1) are selective and show good weed control, with a yield statistically equal to the always clean control.
Urzúa, Medina, de la Rosa, and Fernández (2009) point out that the herbicides Bensulide and Isoxaflutole are selective for husk tomato and show good control of broadleaf weeds and grasses, both in pre-emergence from direct sowing and in post-transplant. In addition, they mention that the herbicide Halosulfuron-methyl (in doses from 7.5 to 112.5 gi.a.·ha-1) is phytotoxic to husk tomato in pre-emergence, and is slightly toxic in post-emergence and post-transplant, so they recommend its use in targeted applications and for the control of weeds such as yellow nutsedge (Cyperus esculentus L.) and other broadleaf species.
Pérez-Moreno, Castañeda-Cabrera, Ramos-Tapia, and Tafoya-Razo (2014) evaluated nine herbicides for weed control in pre-emergence of husk tomato established by direct sowing and with irrigation. They found that the herbicide that caused the least damage to the crop was Bensulide (3.2 %), with 85 % control of broadleaf and narrowleaf weeds in pre-emergence. They also reported that the herbicide Rimsulfuron had the best weed control (98 %), but was slightly toxic (7.5 %). In relation to the herbicide Isoxaflutole, they indicate that it is slightly toxic (12.5 %) in pre-emergence of the direct sowing crop and exhibited regular weed control (75 %).
Few previously reported studies include data on crop yield with different herbicides. Therefore, the objective of this study was to evaluate the effect of three herbicides (Bensulide, Halosulfuron- methyl and Isoxaflutole) on yield and weed control in husk tomato, under the hypothesis that it is possible to find a herbicide that allows designing a weed control strategy for the crop.
Materials and methods
Location of the experiment and crop management
The experiment was established in Chapingo Autonomous University’s Experimental Agricultural Field (19° 29’ 20.4” NL and 98° 52’ 26.7” WL, at 2,250 masl.). Planting was carried out on March 12, 2016 in 200-cavity polystyrene trays with Cosmo Peat® as substrate. After emergence, seedlings were watered every other day, for three weeks, with 50 % Steiner nutrient solution (Steiner, 1984), then the waterings were daily with 100 % Steiner nutrient solution Steiner.
The crop was established in open field conditions by transplanting on April 16, 2016 under a fertigation system in 1.2 m wide furrows. A 16 mm diameter hose with 1.5 L∙h-1 self-compensating drippers and 33 cm dripper spacing was placed in each furrow. Bottom fertilization was applied with the commercial products urea, diammonium phosphate and potassium chloride (100-100-50, respectively). During crop development, 50 kg of urea per hectare were applied each week in irrigation. Nutrition was supplemented with applications of Bayfolan Forte® liquid foliar fertilizer, and pests were controlled with Methomyl.
Manual weeding and the herbicides Bensulide (PREFAR 480-E®, 5.76 kgi.a.·ha-1), Halosulfuron-methyl (SEMPRA 75 GD®, 75 gi.a.·ha-1) and Isoxaflutole (PROVENCE 75 WG®, 112.5 gi.a.·ha-1) were evaluated. Bensulide and Isoxaflutole were applied 10 dat, Halosulfuron-methyl was applied in post-emergence of the weed (21 dat) and manual weeding (always clean control) was done at 21 and 44 dat. The herbicides were applied dissolved in water at a dose of 400 L·ha-1 using a manual sprayer (model 425, Swissmex®) with a hollow cone nozzle. In order to identify the weed species present at the site, an additional never-weeded control was also left in place.
Experimental design and unit
The experimental design was randomized complete blocks with 10 replicates per evaluated treatment. The experimental unit consisted of a 1.2 m wide furrow with 22 plants spaced 33 cm apart.
Yield was quantified from two fruit cuts, the first at 70 dat and the second two weeks after the first. In both cuts, the fruit yield per experimental unit and the weight of a 10-fruit sample were recorded. At the end, the values obtained in both cuts were added to determine the total yield and the average weight of 10 fruits was calculated with the corresponding data obtained in each cut.
The phytotoxicity of each herbicide on the crop was observed, along with the type of weeds that each controlled or not. For this purpose, the species present in the never-weeded control were identified and the number of individuals of each species was counted in the different experimental units where the treatments were applied. With the data obtained, the weed density was calculated as the number of individuals per square meter.
An analysis of variance of the harvest variables was carried out and, subsequently, Tukey’s multiple comparison test (P ≤ 0.05) was performed on the variables that showed a significant effect of the treatments.
The number of individuals of each species, as well as the weed density, was analyzed by the Friedman test (Conover, 1999), with which the three herbicides and the never-weeded control were compared. In each case, multiple comparisons using rank sums were made to identify the best treatment.
Results and discussion
Analysis of variance
Table 1 shows that the treatments had a significant effect (P ≤ 0.05) on yield per plant in cut one (YC1), yield per plant in cut two (YC2) and total yield per plant (TYP). For the weight of 10 fruits in cut one (W10FC1), weight of 10 fruits in cut two (W10FC2) and average weight of 10 fruits in both cuts combined (AW10FBC) there was no significant effect of the treatments (P > 0.05). The coefficients of variation presented values comparable with those obtained in other husk tomato studies, with the exception of YC2 (Peña-Lomelí et al., 2008). This could be due to the fact that in the first cut only completely filled tomatoes were collected (when the fruit fills the calyx or husk), while in the second one the rest of the fruits were cut, which increased the internal variability.
Comparison of means
Table 2 shows the comparison of means test of the yield variables. For YC1, the clean control (manual weed control) and the herbicide Isoxaflutole, statistically equal to each other, were superior to the herbicides Bensulide and Halosulfuron-methyl (P ≤ 0.05), with no difference between the latter two. In YC2, the herbicide Isoxaflutole was the best, although it only significantly surpassed Halosulfuron-methyl. This suggests that Isoxaflutole remained effective in controlling weeds longer. The treatment with this same herbicide had the best total yield, which was statistically equal to the control, although of these two treatments only Isoxaflutole significantly outperformed (P ≤ 0.05) the other herbicides. As can be seen in the same table, no treatment had a significant effect on fruit size (evaluated as W10FC1, W10FC2 and AW10FBC), so the differences in yield can be explained by the fruit set, which should be higher in plants with less competition from weeds.
|Clean control||0.811 az||0.216 ab||1.027 ab||537.2 a||442.2 a||489.7 a|
|Bensulide||0.585 b||0.256 ab||0.841 b||536.3 a||386.3 a||461.3 a|
|Isoxaflutole||0.801 a||0.329 a||1.130 a||538.8 a||373.4 a||456.4 a|
|Halosulfuron-methyl||0.394 b||0.160 b||0.554 c||489.7 a||330.6 a||410.2 a|
In the three yield variables (YC1, YC2 and TYP), the results obtained with Isoxaflutole are markedly superior to those obtained with the other two herbicides, and in no case different from those of the clean control. Therefore, Isoxaflutole can be considered as the best active ingredient for weed control in husk tomatoes, as it was just as effective as manual weeding.
Table 3 presents a list of the weed species found in the never-weeded control and the number of individuals of each species. As can be seen, the most abundant species were buffalobur nightshade, common purslane and red-root amaranth, followed by cheeseweed and coco-grass, while oat and chayotillo were scarce. However, the last one is relevant due to its climbing growth habit, as a single plant can cover a large part of the cultivated area.
|Common name||Scientific name||Number of individuals|
Weed control and selectivity
In the results obtained with the Friedman test (Table 4), it can be seen that in the seven weeds found there was an effect of the treatments on the number of individuals per experimental unit (P < 0.01). When this is found, it is expected that the greatest number of individuals will be in the weed control and that it will decrease with the application of herbicides. Weed density was also affected by the treatments evaluated. Since a significant effect on this variable was found, the desirable treatment will be the one with the lowest density, as this decreases competition for space, water and nutrients.
|Never-weeded control||9||20.5 bz||660||40.0 a||1||16.5 c||737||40.0 a|
|Bensulide||18||30.0 a||331||18.0 c||2||18.5 c||136||19.0 c|
|Isoxaflutole||9||19.5 b||413||27.5 b||7||26.0 b||80||12.0 d|
|Halosulfuron methyl||16||30.0 a||320||14.5 c||29||39.0 a||284||29.0 b|
|Tc||4.7 **||39.3 **||38.1 **||74.3 **|
|Weed density (plants∙m-2)|
|Never-weeded control||977||40.0 a||1143||40.0 a||1101||40.0 a||55.1||40.0 a|
|Bensulide||329||26.0 b||61||22.0 c||103||21.5 c||11.7||22.0 c|
|Isoxaflutole||115||10.0 c||0||10.0 d||0||10.0 d||7.4||10.0 d|
|Halosulfuron-methyl||292||24.0 b||363||28.0 b||226||28.5 b||18.2||28.0 b|
|Tc||84.8 **||131.6 **||208.3 **||131.6 **|
In general, the population of different weed species was reduced with the application of herbicides. For cheeseweed, red-root amaranth, buffalobur nightshade and common purslane, which were the four weeds with the highest number of individuals in the never-weeded control, the best control was obtained with Isoxaflutole; consequently, this efficiency resulted in a lower weed density (Table 4). For its part, the coco-grass population decreased almost by half with the application of both Bensulide and Halosufuron-methyl. In the case of oat, the treatment with Isoxaflutole yielded the same number of individuals as the never-weeded control, while with Bensulide and Halosulfuron-methyl it doubled, which is contrary to expectations. A similar phenomenon occurred with chayotillo, as the number of individuals of this species was not statistically different between the never-weeded control and the Bensulide treatment, but increased slightly with Isoxaflutole and grew drastically with Halosulfuron-methyl.
In the last two species described, the increase in the number of individuals with some treatments is explained by the fact that these herbicides are not effective in controlling those particular species, but they are for others. Therefore, when the competition of the species in question is eliminated, they can be developed more fully. The most drastic case occurred with Halosulfuron-methyl on chayotillo, as it is highly invasive due to its climbing growth habit, and in this case the number of individuals grew to such an extent that the plots were practically covered.
Description of the behavior of each herbicide
Provence 75 GD® (Isoxaflutole). This herbicide was applied in post-transplant in a band and directed to the base of the plant. When applied in pre-emergence of the weeds, it showed good control of broadleaf weeds, but did not control oat or coco-grass, and had partial control of chayotillo, which could be due to the escape caused by band application. The use of this herbicide in husk tomato is safe, since it was applied on the row of plants and did not show any damage, which makes it selective for this crop in post-transplant, which coincides with what was reported by Pérez-Moreno et al. (2014). An additional observation is that in the area where the herbicide was prepared and the spray backpack was calibrated, there were grasses, which died after the application, so its effectiveness in the control of grasses is evident.
Prefar 480 E® (Bensulide). Its application was made in a band directed to the base of the plant and in the borders of the row of plants. This herbicide efficiently controlled chayotillo, but did not control oat, and had partial control of broadleaf weeds (cheeseweed, red-root amaranth, buffalobur nightshade and common purslane) and coco-grass. There was no damage to the crop, as also reported by Pérez-Moreno et al. (2014) and Roque et al. (1995).
Sempra 75 GD® (Halosulfuron-methyl). In general, it did not show good weed control and was toxic to the husk tomato when it was applied on the plant. In particular, it had an effect on coco-grass, so it is a valuable product for the control of this weed in the husk tomato, as long as it is applied in a band and directed to the base of the plant, as also suggested by Urzúa et al. (2009).
Strategy for weed control in husk tomato
Husk tomato is a crop sensitive to excess moisture in the soil, a condition in which it is attacked by fungi such as Fusarium oxisporum; therefore, it is necessary to make two crops and a hilling in order to promote aeration of the roots, in addition to controlling weeds between plant rows, but not within them. In this context, a strategy for effective weed control in husk tomato established by transplant could consist of the following: make a total application of Isoxaflutole in pre- or post-transplant, carry out three cultivation tasks and after the third one (approximately 40 dat) apply the herbicide in a band to "seal" the soil. It is essential that the soil has sufficient moisture or is irrigated after application to ensure that the herbicide acts efficiently. For rainfed conditions it is recommended to apply the herbicide after a rain. In soils where coco-grass is a major weed, it is recommended to apply Isoxaflutole plus Bensulide or Halosulfuron-methyl in pre-transplant.
It is important to note that Isoxaflutole is not sold in Mexico, but can be imported as Provence 75 GD® from Brazil or as Merlin 75 GD® from Central America, where it is used in sugarcane.
The herbicide with the best chemical control of weeds in husk tomato was Isoxaflutole, since it significantly reduced the population of most of the weeds found and did not affect the yield with respect to the always clean control.
Isoxaflutole is a selective herbicide for husk tomato, although it does not control coco-grass (Cyperus esculentus L.) or oat (Avena sativa L.), and only partially controls chayotillo (Sicyos deppei G. Don).
The alternatives for controlling coco-grass in husk tomato are Bensulide and Halosulfuron-methyl, although the latter is not selective to tomato and must be applied in a band.