This week, the overall grades of four Chemicals stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

China Green Agriculture’s (NYSE:CGA) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. China Green Agriculture engages in the research, development, production, and sale of various types of fertilizers and agricultural products in the People’s Republic of China. The stock price has dropped 7.5% over the past month, worse than the 1.4% increase the S&P 500 has seen over the same period of time. To get an in-depth look at CGA, get Portfolio Grader’s complete analysis of CGA stock.

DuPont’s (NYSE:DD) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Dupont is involved with science and innovation across a range of disciplines, including agriculture and industrial biotechnology, chemistry, biology, materials science, and manufacturing. The stock gets F’s in Earnings Growth, Earnings Revisions, Earnings Surprise, and Sales Growth. For a full analysis of DD stock, visit Portfolio Grader.

Slipping from C to a D rating, Praxair (NYSE:PX) takes a hit this week. Praxair supplies gas to industries primarily located in North and South America. For more information, get Portfolio Grader’s complete analysis of PX stock.

Olin Corp.’s (NYSE:OLN) rating weakens this week, dropping to a D versus last week’s C. Olin Corporation manufactures and sells chlorine, caustic soda, sodium hydrosulfite, hydrochloric acid, hydrogen, sodium chlorate, bleach products, and potassium hydroxide. To get an in-depth look at OLN, get Portfolio Grader’s complete analysis of OLN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.