WEED CONTROL IN NEWLY ESTABLISHED ALFALFA

Transcription

1 WEED COTROL I EWLY ESTABLISHED ALFALFA } W. D. MClellan, v. Shweers, J. Hill and D. Tisher Tulare County Farm Advisors, Extension Weed Sientist and Staff Researh Assoiate, resetively Weed ontrol in newly established alfalfa is not an easy task. and the best method of ontrol will vary from grower to grower. In the Central Valley. alfalfa is lanted from Otober to Marh and the weed roblems in seedling alfalfa vary with the lanting date. revious roing attern. and management raties. Cultural and hemial alternatives are available to the grower to assist him in getting the best stand establishment ossible A vigorous ometitive seedling stand rovides the most sound basis for good weed ontrol and rofitable alfalfa rodution. Good weed ontrol in revious ros is one of the best methods of minimizing weed ressure in seedling alfalfa. Preirrigation and subsequent working of the ground allows the rearation of a more desirable seedbed and hels to redue the weed seed oulation Herbiides are imortant "tools" to ontrol weeds in seedling alfalfa stands; however, if the grower relies entirely on hemial ontrol in seedling alfalfa, the results may be less than satisfatory. Herbiides will not substitute for good land rearation and a relant irrigation. Table I lists weed susetibility for ertain herbiides registered for use in seedling alfalfa. Although many re and ostlant herbiides are resently available for weed management in seedling alfalfa, there is little information available on their erformane in relation to the rodution and ersistene of the alfalfa lant in the field. Reorted here are the results of trials examining the effet of re and ostlant herbiides in fall and sring lanted alfalfa on: (1) ontrol of weeds; (2) yield of alfalfa and weeds; and (3) stand ersistene. MATERIALS AD METHODS Sring Planting: } Herbiides were alied relant to a sring seeding of alfalfa on the Lerda Ranh near Tulare, California. The variety Joaquin II was broadast February 27, 1976 at a rate of 18 lbs/a. The soil tye was Chino lay loam. The lot design was a randomized omlete blok with eah of the five treatments reliated four times. Individual lots were 2' x 8' in size. The herbiide treatments and rates used are the same as the relant treatments given in the fall lanting. Fall Planting: Herbiides were alied relant to a fall seeding of alfalfa (Otober ls. 1976) on the W. George Ranh. Strathmore, California. The variety was WLSO8 and the soil tye was Cajon fine sandy loam. The lot design was a randomized omlete blok with eah treatment reliated 6 times. Individual lot size was 27' x 44'. Postlant herbiides were alied in February when most of the broadleaf weeds were less than 3" in diameter. These treatments were alied as sublots on to of the relant lots in a randomized slit blok design. Eah treatment was reliated 6 times with an individual lot size of 27' x 3'. The herbiide treatments and rates used were as follows: Prelant Postlant 2 3 Untreated ontrol Benefin (Balan@) -1.5 lb ai/a EPTC (Etam@) -3. lb ai/a Untreated ontrol 2,4-DB ester -1. lb ai/a Dinoseb, Ammonium@salt 4 {Dow Seletive) -1. lb ai/a Green ho {early harvest) t -51-

2 These materials were alied at the above rates in 2 gallons of water er are. The herbiides were inororated with a double dis and harrow to a deth of 3 to5 inhes. Yields reorted here reresent 12' x 4' harvested areas in the sring lanting and 3' x 25' harvested areas in the fall lanting from eah lot with the yields adjusted to % moisture. Within eah lot were three areas from whih stand ounts, lant growth and weed ometition data were obtained. RESULTS Setrum of Weeds: Sring -The major grass weeds resent were watergrass (EhinohZoa s.), foxtail (Setaria s.), and ugrass (EriohZoa s.). The redominant broadleaf weeds were lambsquarters (Chenoodium s.), igweed (Amaranthus s.), wild lettue and others. Fall -The major weeds were sheherdsurse (CaseZ bursa-astoris L.), London roket (Sisymbrium irrio L.). Other weeds inluding fiddlenek and lambsquarters were resent to a minor extent. Yield Data. In the sring lanting both Etam@ and Balan@ were effetive in suressing weed ometition in the first, seond and subsequent harvests (Fig. 1 and 2). In the untreated ontrol lots the grasses (eseially watergrass) beame established early and rovided heavy ometition for the alfalfa lant throughout the season (see Weed Control in Seedling Alfalfa, W. D. MClelland and V. Shweers, Sixth California Alfalfa Symosium, for omlete data). Although the yields of alfalfa alone were signifiantly higher in the herbiide treated lots, the total seasonal yield of alfalfa hay (alfalfa and weeds was highest in the untreated ontrol (Table I). In the fall lanting the relant herbides did little to redue the amount of weeds resent in the first harvest. However, Etam did initially suress the develoment of sheherdsurse. This aarently allowed the alfalfa lants to develo and grow well in site of later weed ressure. The Etam@ treatment had the highest yields of alfalfa alone among the relant treatments in the first harvest. The use of ostlants in a fall lanting (Fig. 3) showed that both 2,4-DB ester and dinoseb (dinitro on the grah) were effetive in suressing the weed oulation. It should be noted that 2,4-DB ester aused some stunting of the alfalfa lant rior to the first utting and resulted in some yield redution. Green hoing, a ratie used by many growers, redued the amount of weeds, but the early utting also redued the alfalfa yield in the first harvest. In the seond harvest (Fig. 2 and 4) none of the treatments resulted in signifiant yield differenes and subsequent harvests followed this attern. Very few weeds develoed in this field after the first utting. The total seasonal yield of alfalfa hay was highest in the untreated ontrol (Table 11). Stand Psi-se: Stand ersistene is an imortant art of any alfalfa weed study (Fig. 5). In the sring lanting the early heavy weed ressure in the untreated ontrol resulted in signifiant redution in seedling stand establishment and the effet of the weeds on stand ersistene ontinued throughout the season. The number of alfalfa rowns er square foot in the fall lanting were higher in the best herbiide treatment initially, but as the season rogressed, the differenes were eliminated. SulTIIIary: The data resented here suort grower and researher observations that herbiides, when roerly hosen and used in addition to good management raties, an suress weed ometition in seedling alfalfa. In the sring lanting when grasses (eseially watergrass) rovided heavy weed ressure, alfalfa yield and stand ersistene were affeted. Prelant herbiides were effetive in suressing weed ometition. In the fall lanting both relant herbiides -52-

3 and were ineffetive in reduing the amount of weeds in the first harvest. The ostlant herbiides were effetive, although 2,4-DB ester did ause some stunting of the alfalfa lant's growth. Most of the weeds in the fall lanted alfalfa were not evident until after the alfalfa had emerged and good seedling growth had begun. These seedlings tolerated heavy weed ometition from sheherdsurse and London roket through the first harvest. The subsequent harvests and stand data indiated that the initial weed ressures affeted neither yield of alfalfa nor stand ersistene. Table II gives a summary of fall vs. sring lanted alfalfa. Sring lanted alfalfa has two less harvests than the fall lanting. The yield of alfalfa alone is 3 to 4 tons er are less than what may be obtained from a fall lanted first year yield. Under heavy grass infestations sring lanted alfalfa showed redued vigor and hay yields refleted a high erentage of weeds. In the San Joaquin Valley good management raties utilizing roer land rearation, reirrigation and the judiious use of a good weed ontrol rogram will lead to exellent alfalfa stand establishment. Growers who are disaointed with their yields, stand ersistene and weed ontrol in sring lanted alfalfa may want to onsider lanting in the fall as one alternative. Aknowledgments: We gratefully aknowledge the assistane rovided by J. Lerda. Tulare And W. George. Porterville. Dairymen's Creamery Cooerative Assoiation. Agri-Teh Analytis. Stauffer Chemial and Elano ooerated in these trials. Tehnial assistane inluded M. Bailey. G. Weinberger and D. Henson. This artile should be onsidered as a rogress reort and not a reommendation by the University of California. -53-

4 TABLE I: A WEED SUSCEPTIBILITY CHART FOR CERTAI SELECTIVE HERBICIDES USED I SEEDLIG ALFALFAl Herbiides Prelant Postemergene Broadleaf benefi Balan roflurain EPTC@ roham@ Tolban Etam.Chem Hoe dinoseb 2.4-DB* 2.4-DB* Seletive ester amine hikweed ontnon fiddlenek groundsel C C C P P P C C C C C P P filaree knotweed lambsquarters London miners mustard roket lettue nightshade igweed sheherdsurse sowthistle wild radish Grasses annual barnyardgrass anarygrass bluegrass foxtail volunteer wild oat barley ereal yellow nuts edge 1 * C = ontrolled, = artially ontrolled, = not ontrolled Restrited herbiide; ermit required from County Agriultural Commissioner -54-

5 TABLE 11: EFFECT OF WEED COTROL I SEEDLIG ALFALFA O FIRST SEASO YIELDS. Yields are exressed as lb{a at % moisture. First Season Yields (lb/a} Planting date Weedl ontrol umber harvests Alfalfa Weeds Total Sring 1976 o , Sring 1976 Yes , Fall 1976 o , Fall 1976 Yes Weed ontrol -this reresents the herbiide treatment that gave the best weed ontrol in our trials. -55-

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7 Poonds Fer Are :x> - - (D... o - "ib"' < (1) (/) G)... (I) (I) C'D (I) ) -57.

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9 - a "2. 1 I

10 Crowns Per Square Foot -6-