From David Montejano, Anglos and Mexicans in the Making of Texas, 1836-1986, ch. 4, “Race, Labor, and the Frontier.” 76-79
On the Mexican Frontier.
For several decades after annexation, life along the border continued in much the same way as before. Even as the American mercantile elite displaced Mexican rancheros and money-poor landed elite from their land, the life of landless Mexicans, the peones and the vaqueros, remained generally unaffected. The cattle hacienda remained the dominant social and economic institution of the border region, and the work relations that linked Anglo patrón and Mexican worker remained paternalistic and patriarchal. The development of a cattle industry required no fundamental changes in traditional labor relations. The longevity of the hacienda as a social institution was due  to its resiliency: finding a market, it would respond and produce; lacking one, it would turn inward and become self-sustaining.
Beyond the ranch economy, however, Anglo and European pioneers who wished to experiment with such money crops as cotton or cane were severely limited by the scarcity of day laborers. Mexican workers were viewed as unreliable because many still owned small tracts of land and worked only to supplement their meager incomes. Mexican rancheros devoted themselves to cultivating corn, the most important subsistence crop in their diet.. Once subsistence needs were met, Mexican rancheros turned to raising cattle, which was more profitable than farming. The Abbé Domenech never could understand how a ranchero of the lower border lived,
for he labours little or none; the very shadow of labor overpowers him, and he comprehends not activity, save in pleasures. The wonderment was largely rhetorical, however, for the abbé provided the answer to his own question. The ranchero‘s work in tending to
herds of oxen, horses, goats, and sheep required very little labor,
and therefore does he like it so much. Thus, few Mexicans were willing to pick cotton or cut cane.
On the other hand, the masterless, ex-peón population present in Texas may have refused to have anything to do with plantation labor. These ex-peones were not just those left behind by the refugee elite of Texas, but comprised also those who fled peonage in northern Mexico. Escape to Texas at times reached such critical proportions that cotton cultivation in the neighboring state of Tamaulipas was threatened. The possibility of escape weakened debt peonage on the Mexican side, much as it had weakened American slavery on the American side. During the fifteen-year period (1845-1860) between the Mexican War and the American Civil War, the Texas-Mexican border was the boundary sought by both escaping Mexican peones and black slaves. The boundary was also the working zone for slave and peon
Given these circumstances, far less cotton was cultivated in the Lower Rio Grande Valley in the decade after the Mexican War than in the preceding period under Mexican rule. American expansionist interests, as historian Graf noted, argued that the Mexican laborer was unreliable because he was
accustomed to compulsory labor in his own country if he did not have his own little piece of ground. Large-scale planting was impossible because under the
free labor conditions of Texas Mexicans worked only to satisfy their needs, which were few. According to this reasoning, there were two ways in which a permanent labor supply could be secured in the Lower Valley: (a) if  the United States controlled both sides of the Rio Grande, black slave labor could be introduced with safety and large-scale plantations begun, or (b) if there was a
peón law for western Texas, local authorities would have the power to compel the Mexicans to work and <q>thereby ensure the farmer a steady labor supply, as well as reduce vagrancy. The Civil War, which followed shortly after these proposals were offered, made these questions moot.
[…] While Mexicans proved reluctant to perform farm labor, work on  the ranches continued to be meditated [sic] by the old practice of debt peonage. Although peonage was formally illegal, most men and women on Texas ranches nevertheless looked to a patrón to provide them with the necessities of life, to give them work, to pay them wages, and, finally, to donate a jacal and provisions when they grew too old. In return there was a loyalty to the ranch and its owners that acknowledged and repaid a patrón‘s sense of noblesse oblige.
Graf, LeRoy P. “The Economic History of the Lower Rio Grande Valley, 1820-1875.” 2 vols. Ph.D. dissertation, Harvard University, 1942.